…of Old School BMX Parts, Technical Terms, Abbreviations and Slang



(A work in progress, this glossary is a fluid document that is constantly being updated and added to – feel free to contact me if you’d like to see any particular terms included)



1/8″ chain: Chain size is specified by pitch and width. The pitch is the distance between rollers (1/2″ on all modern bicycle chains). The width is the internal width where the sprocket teeth fit. An 1/8″ width chain is used on most single-speed bicycles, including BMX.


1020, hi-ten, high tensile or mild steel: Hi-tensile steel is a cheaper form of tubing than chromoly steel. It’s not as strong as chromoly so to get the same amount of strength in the bike the tubes must be thicker, meaning a hi-ten bike will be heavier than a chromoly bike. The aesthetic difference between a hi-ten steel frame and a chromoly steel alloy frame is in the quality of the welds. The MIG welds on a Hi-Ten frame are generally chunkier, more irregular with occassional splattering, where as TIG welds form a chain of smooth uniform semicircles, like perfectly repeating waves.


1pc Cranks: With a one-piece crank and bottom bracket, the spindle and crank arms are a single piece. The bottom bracket shell needs to be large enough to accommodate removal and installation of this S-shaped crank, hence they fit only frames with ‘American’ sized bottom brackets. Bearing cups are pressed into the bottom bracket shell which, in the case of 1pc cranks, most commonly houses loose ball or caged bearing systems which require more maintenance that the sealed bearing systems readily available for 3pc cranks. When installed the 1pc crank holds the cones, facing in; adjustment is made via the left-threaded non-drive side cone. One piece cranks require pedals with 1/2″ threaded axels (when installing, remember that left side pedals are reverse threaded).


3/32″ chain: Chain size is specified by pitch and width. The pitch is the distance between rollers (1/2″ on all modern bicycle chains). The width is the internal width where the sprocket teeth fit. A 3/32″ chain is predominantly used on derailer equipped bicycles that have more than 3 cogs at the rear.


3pc Cranks: With three-piece cranks the bottom bracket spindle is separate from the crank arms which allows for more strength and rigidity, particularly beneficial when racing or performing tricks that put stress on the drive train. In a 3pc system the crank arms attach to the spindle via a common square taper, a cotter or via a variety of splined interfaces. Three piece cranks require pedals with 9/16″ threaded axels (when installing, remember that left side pedals are reverse threaded).


4130, crmo or chromoly steel: Chromium-molybdenum, a high strength steel alloy which can be made into lightweight tubing with very thin wall gauges, used in manufacturing high quality frames.





Aero tubing: An elliptical tube design used on many higher end chromoly old school race bikes.


Aluminium (or aluminum in the US) frames: 6061 aluminium and 7005 aluminium are the most common aluminiums used for bike frames. Welded aluminium frames started to appear in the marketplace only after this TIG welding became economical in the 1970s. Aluminium has a different optimal wall thickness to tubing diameter than steel. It is at its strongest at around 200:1 (diameter:wall thickness), whereas steel is a small fraction of that. However, at this ratio, the wall thickness would be comparable to that of a beverage can, far too fragile against impacts. Thus, aluminium bicycle tubing is a compromise, offering a wall thickness to diameter ratio that is not of utmost efficiency, but gives us oversized tubing of more reasonable aerodynamically acceptable proportions and good resistance to impact. This results in a frame that is significantly stiffer than steel.


Anodised: Anodising is the electrochemical conversion of the surface of aluminium to an aluminium oxide. This coating is extremely hard (aluminium oxide is used for grinding wheels). And can be coloured by either organic dyes or inorganic metal compounds. Many higher quality vintage racing BMX parts (and some frames, ie. Race Inc or the PK Ripper) are manufactured from aluminium and anodised for protection and aesthetics. Aluminium parts can be de-anodised using a bath of caustic soda, and re-anodised by professionals.





Baseball (re: serial #): The mark of a quality Japanese frame or part made by Koizumi (ie. early Diamond Back Cobra and Hutch)


Bearing race: Sometimes referred to as ‘cups’, bearing races are essential components of both the headset and bottom bracket. Each bearing race seats either loose ball or cartridge bearings that allow the cranks and fork steerer to rotate smoothly.


BITD: Acronym for the phrase ‘back in the day’, commonly used on vintage bike forums.


Boat anchor: Oldschooler slang for a bike or frame deemed heavy, badly designed, of poor quality, usually with an undesirable brand name and not worth saving.


Bolt Circle Diameter (B.C.D.): On a crankset, the diameter of the circle formed by the chainring bolts. The most common old school BMX 5 bolt B.C.D.s are 130 mm or 110 mm diameters. To find out the B.C.D. of the chainring or spider you have measure centre to centre between two adjacent holes, then multiply that measurement by 1.701 (or just use Sheldon Brown’s cheat sheet:


Bottom bracket: Commonly abbreviated to ‘BB, the bottom bracket on connects the crankset to the bicycle and allows the crankset to rotate freely. It is not a bracket as such. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks. The bottom bracket fits inside the bottom bracket shell, which connects the seat tube, down tube and chain stays as part of the bicycle frame.


Bottom Bracket Shell: The bottom bracket shell is a short and wide tube, relative to the other tubes in the frame, that runs side to side and holds the bottom bracket.


Brake Bridge: The short length of tubing or plate connecting the seat stays just above the tire. This is the usual mounting point for a rear caliper brake.


Butted tubing: Among steel frames, using butted tubing reduces weight and increases cost. Butting means that the wall thickness of the tubing changes from thick at the ends (for strength) to thinner in the middle (for lighter weight).





Campy: A nickname for Campagnolo bikes and parts.


Cantilever brake: A cantilever brake has two separate arms, or cantilevers, one on each side of the rim. Each arm pivots on an independent boss attached to the frame or fork, and the two arms are usually coordinated and linked by a transverse (or straddle, or crossover) cable that runs above the top of the tire. The transverse cable is commonly connected to the main brake cable by a yoke.


Carpet queen: Oldschooler slang for a bike that has been built or restored for show only, never to be ridden. Often these bikes have been built to factory spec with NOS parts.


Chainring: A type of ring shaped sprocket specifically designed to be bolted to a ‘spider’ rather than directly to the cranks arms themselves. The benefit of a chainring over a conventional sprocket or chainwheel is ease of interchangeability for different gear ratios. For information on interchangeability and spider compatibility see B.C.D. or Bolt Circle Diameter.


Chain stays: The chain stays run parallel to the chain, connecting the bottom bracket shell to the dropouts.


Chain tensioners: A chain tensioner or ‘banjo bolt’ is a device used to adjust the chain tension on a BMX by pulling back and locking on the rear axle using threaded adjusters to increase tension on the chain the desired amount. Most commonly used on racing BMXs where chain tension is paramount, more so than freestyle.


Chain tool or chain breaker: A tool used to press the rivet pin of a chain partway out of a link, in order to disconnect or ‘break’ a chain to shorten it prior to installation or to remove it.


Chequebook collector: Oldschooler slang for a collector whose goal is predominantly to seeks out rare, NOS parts or ‘factory’ spec bikes, regardless of price, for show only. As opposed to those who value both used and more affordable parts, enjoying hands on building, restoring, customising and riding their bikes.


C.N.C.: Computerized Numerical Control. This refers to modern milling machines and other machine tools that can carve complex parts from solid billets. Although CNC parts are not as strong as forged parts, they can be made into more complicated shapes than is possible with forging or conventional casting. Without the need for moulds, C.N.C. manufacturing techniques are advantageous for shorter or one off product runs.


Crank puller: The threaded tool required to remove 3pc cranks by separating the drive side crank arm from the spindle.


Chroming or electroplating: Electroplating is the application of electrolytic cells in which a thin layer of metal is deposited onto an electrically conductive surface. Chromium or ‘chrome’ plating, the most common type of electroplating used on bike frames and parts, improving both the appearance and also protecting the raw metal beneath from oxidisation. The trick to a perfect chrome finish is in the surface preparation and polishing.


Coaster Brake: A type of rear hub which incorporates a brake which is operated by pedaling backward. It is called a ‘coaster brake’ because it combines the functions of the brake and freewheel (aka ‘coaster’) in a single unit. The most common manufacturers of BMX coaster brakes were Suntour, Bendix and Shimano – parts for which can still be sourced for refurbishment of older BMX hubs running coaster brakes.


Comp III: Perhaps the most famous BMX tire and tread design. Mitsuboshi developed and produced the Competition III tire with guidance and design input from Tioga. Before the Comp-III, most BMX tire designs were based on motorcycle motocross tires. The Comp-III tire was the first tire designed exclusively for the specific needs of BMX. The result was a tread pattern unlike any other with undeniable performance benefits.


Comp IV: The Comp IV tire was the follow up to the Comp III, it was foldable and had a more spaced out tread pattern with smaller tread blocks, it’s popularity was not as long-lived as the Comp III due to the Comp IIIs compatibility with a greater variety of terrains.


Cotterless Cranks: The modern type of three-piece crankset. Although one-piece cranks don’t use cotters either, the term “cotterless” normally refers to two-piece or three-piece sets.

The bottom bracket spindle (axle) used with a standard cotterless crank has tapered square ends, which fit into matching tapered square holes in the cranks. The ends of the axle are threaded, either male or female, and a bolt or nut (called the “fixing” bolt/nut) pulls the crank tightly onto the end of the axle. The nut or bolt head is recessed into the crank, in a hole with threaded sides. These threads can hold a decorative cap that hides the fixing bolt/nut, but their main function it to provide a purchase for the “crank puller”, a special tool that is needed to remove the crank from the axle.


Cottered Cranks:Rarely found on BMX setups, cottered cranks are an old design that use wedge-shaped fasteners called “cotters” to hold the cranks onto the bottom bracket axle. These cotters have a nut to hold them in place after they have been driven or pressed in. They can be difficult to remove, especially if they have been in place for a long time.


CW style handlebars: A particular style of BMX handlebar, designed by the company CW, in which the crossbar lies atop handlebars as a continuous piece of tubing extending from grip to grip.





Down tube: The down tube connects the head tube to the bottom bracket shell.


Drilled or undrilled forks: ‘Drilled’ forks are forks that have had a hole drilled through the crown of the fork for the purpose of fitting a side pull brake caliper. ‘Undrilled’ forks, often considered desirable collectors items among vintage racing BMX enthusiasts are forks that have never had a brake mount hole drilled.


Dropouts: A dropout is another name for a fork end – the slot in a bicycle frame or bicycle fork where the wheel axle is attached. NB: Although the ‘dropout’ has become synonymous with BMX fork ends, the term has in fact been misappropriated when referring to the rearward facing fork ends of track or MX bikes, as technically a ‘dropout’ only refers to fork ends that allow the rear wheel to be removed without first derailing the chain.





Fillet brazing: Fillet frame tubes are precisely notched or mitred and then, while precisely aligned into a jig and fixed in place until complete, a fillet of brass is brazed onto each joint, similar to the lugged construction process, but without the need for lugs. A fillet braze frame can achieve more aesthetic unity (smooth curved appearance) than a welded frame.


Floval tubing: Oversized aluminium tubing with a flattened oval shaped profile. The term ‘floval’ (derived from ‘flat oval’) was originally coined by S.E. Racing founder Scot Breithaupt when the famous aluminium floval tubed P.K Ripper race frames, and its prototype predecessor the BD-III, were first designed and manufactured in 1978/79. Floval aluminium tubing is now commonly used for modern race BMX frames.


Freestyle standers, extenders, platforms and pegs: Welded or bolt-on frame or fork modifications that create a foot or hand hold for use in freestyle tricks. Frame standers are most commonly found on chainstays, behind the seatpost and on the forks either threaded into the fork legs, or onto the axles (known as pegs or spinners).





Goose: Abreviation or nickname for Mongoose bikes and parts.


Gusset: A gusset is a metal plate welded to the frame to increase strength in certain areas. The most commonly gusseted area on a vintage BMX is where the top and down tubes meet the head tube. They can also be found near the bottom bracket between the down tube and the seat tube, and under the down tube where it meets the head tube. The size and shape of gussets is often very useful in determining the make and model of a vintage frame.


Gyro system: The Odyssey Gyro, ACS Rotor or Skyway Spinmaster are all branded design variations of a system that attaches between the stem and headset of a freestyle bike to allow the handlebars to spin freely without the restriction of brake cables to the red caliper becoming tangled around the frame.





Headset: The headset is the set of components that provides a rotatable interface between the fork and the head tube of the frame. A typical headset consists of two cups that are pressed into the top and bottom of the headtube. Inside the two cups are bearings which provide a low friction contact between the bearing cup and the steerer.


Head tube or steerer tube: The short tube at the head of the frame that houses the headset through which the steerer of the fork passes.





Kuwi: A nickname for Kuwahara bikes and parts.





Lugged frames: A classic type of construction for vintage bike frames which uses standard cylindrical steel tubes connected with lugs. Lugs are fittings made of thicker pieces of steel. The tubes are fitted into the lugs, which encircle the end of the tube, and are then brazed to the lug. Historically, the lower temperatures associated with brazing (silver brazing in particular) had less of a negative impact on the tubing strength than high temperature welding, allowing relatively light tube to be used without loss of strength. Advances in metallurgy (“air hardening”) created tubing that is not adversely affected, or whose properties are even improved by high temperature welding temperatures, which has allowed both TIG & MIG welding to sideline lugged construction making the mass production of vastly more efficient. Lugged frames are considered easier to repair than welded frames due to their simple construction.





Master link: A special chain link designed to be easily disassembled and re-assembled.


MIG welds: Metal inert gas (MIG) welding is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece metal, which heats the workpiece metal, causing them to melt, and join. Frame tubes are precisely aligned into a jig and fixed in place until the welding is complete, eliminating the need for lugged construction. MIG welds are typically the hallmark of cheaper mild (hi-ten) steel frames and the appearance of MIG welded joints and seams is generally considered less aesthetically pleasing than TIG welds.


Monocoque: Monocoque, meaning ‘single shell’ in French, is a frame design that utilises the external skin to support some or most of the load. Built as a hollow shell, without an interior framework, the strength of a monocoque structure comes from the shell alone. The Haro Monocoque of the mid ’90s pioneered this type of frame design in BMX, heavily influencing the frame designs in modern BMX racing.


Motomag: An early Mongoose BMX (1975-81) named for its unique 5 spoke webbed design alloy mag wheels.





NJS: Nihon Jitensha Shinkokai – the stamp of the Japanese Bicycling Association – indicating certification as the gold standard in Japanese made road, freestyle and BMX bike parts.


NOS: Acronym for the phrase ‘new old stock’, commonly used on vintage bike forums. Applies to parts that have never been fitted, modified, refinished or tampered with.



OG: If you’re thinking ‘original gangsta’ You wouldn’t be wrong to assume this refers to an ‘original gangsta’, as it more commonly does in pop culture. But on vintage bike forums this is an abbreviation for ‘original’. In popular culture





Potts’ mod: Invented by Steve Potts in 1984, the ‘Potts’ Mod’ a hollow-bolt system for the front brakes. It enables riders to turn their bars without the front brake getting tangled around the handle bar. The front brake cable is fed from the lever, down through a hollow quill bolt in the stem, out the fork crown, doubling back up the fork leg and into the front caliper from the bottom up. The front caliper must be setup specifically to work with a Potts’ Mod.


Powder coating: Powder coating is a type of frame surface treatment that is applied as a free-flowing, dry powder. The main difference between a conventional liquid paint and a powder coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form. The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a “skin”. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. The properties of different colour pigments can affect the flow of the powder sometimes leading to variations in finish between different powder coat colours.





Quill stem: A quill stem requires a set of forks with a threaded steerer tube which does not extend above the headset. The quill stem fits down into the inside of the top of the fork steerer tube to be held in place internally via either a wedge and bolt or cone shaped expander nut and bolt. When choosing a quill stem for your old school build be sure to measure the internal diameter of your head tube to ascertain whether you require a 21.2mm or 22.2mm sized stem.





Radial spoking: The oldest and simplest of spoke patterns. The spokes run straight outward from the hub to the rim. This is called “direct” or “radial” spoking.


Rake: The “rake” or “offset” of a fork is the distance between the wheel axle and the extension of the steering axis. This may be accomplished by bending the fork blades, or by attaching the fork ends to the front of the blades, or by tilting the blades where they attach to the crown. Rake is one of the three factors that affect the trail of the bicycle, which has a considerable influence on the handling qualities.


Ratchet: A mechanism which will rotate freely (“freewheel”) in one direction, but either will not turn the other way, or will drive some other part when turned the other way. A bicycle’s freewheel has a ratchet which causes the sprocket to turn the wheel forward when the rider pedals forward, but allowing the wheel to turn forward even when the pedals are not being turned.


Repop: Also ‘repro’, is a slang abbreviation for the reproduction of an original part that had previously been decommissioned. Repop can be used to describe both products that have been recommissioned by the original manufacturer, or reproduced be another entity or individual.


Reynolds: Reynolds, currently known as TI/Reynolds, is an old and very highly regarded maker of bike tubing. Reynolds pioneered the techniques of making butted tubing around 1900, and its 531 (say “five, three, one”) manganese-molybdenum alloy tubing was the standard of excellence for many decades. Newer formulations from Reynolds include 753 and 853.





Seat stays: The seat stays connect the top of the seat tube (often at or near the same point as the top tube) to the rear fork dropouts.


Seat tube: The seat tube accommodates the seatpost of the bike, which then connects to the saddle. The seat tube commonly protrudes just above the connecting top tube and seat stays, and down to connect with the bottom bracket shell.


Spider: A spider is the multi-armed part of a crank, or crank arm attachment, to which a chainring is attached. 4 and 5 arm configurations are most common and a uniform Bolt Circle Diameter system is used to define chainring compatibility.


Sprocket or chainwheel: A toothed wheel or gear that is part of a chain drive. The front or main sprocket is also commonly called a chainwheel or chainring. The term “sprocket” can refer to either front or rear, but most road and track cyclists use this term mainly to refer to their rear sprockets. The use of “sprocket” to refer specifically to a chainwheel is predominantly confined to BMX usage.


Steerer: The steerer or steering tube is the part of the fork that extends upward from the fork crown, and into which the handlebars attach (via a stem) allowing the user to steer the bicycle. The steerer of the fork interfaces with the frame via the headset.


Stem: Sometimes referred to as ‘head stem’ or ‘gooseneck’, the stem is the component that connects the handlebars to the steerer tube of the fork. The stem’s design may utilise either a quill (old school/mid school) or threadless (mid school/new school) system of attachment to the steerer, and each system is compatible with respective headset and fork designs:





Threadless stem: Threadless stems feature a modular design that works with threadless forks by clamping around the part of the steerer tube that extends above the headset. With threadless stems, a ‘star-nut’ is driven down into the threadless steerer tube and held in place by two barbed flanges. The top cap bolts into, and pulls against, the star-nut, thereby preloading the headset bearings.


TIG welds: Tungsten Inert Gas (TIG) welding, is an arc welding process that uses a nonconsumable tungsten electrode to produce the weld, most commonly used in the manufacture of chromoly and aluminium frames, and also used to weld stainless steel and other alloys. Frame tubes are precisely aligned into a jig and fixed in place until the welding is complete, eliminating the need for lugged construction. The more aesthetically desirable appearance of even and consistent ‘ladder’ pattern TIG welds are considered a symbol of status on a bike frame and an indicator of quality tubing and manufacture.


Trail: The distance from the center of the contact point of the front wheel with the riding surface to the intersection of the steering axis (head tube) with the surface. The trail is a function of the head angle, the fork rake, and the tire diameter. Trail has a major effect on the handling of a bicycle. More trail increases the bicycle’s tendency to steer straight ahead. A bicycle with a largish trail dimension will be very stable, and easy to ride “no hands”. A bicycle with a smaller trail dimension will be more manuverable and responsive.


Trik Topz: The most famous old school brand name in novelty valve caps, still going strong today. The term Trik Topz (or trick tops) is often used in the OS BMX scene to refer to any novelty valve cap, not specifically those made by the Trik Topz brand.


Tri-moly: Trimoly was a term coined for frames constructed of a chromoly front triangle (top tube, down tube, seat tube) with hi-ten steel seat stays and chain stays. This particular trend in manufacturing grew out of a desire to make a level of chromoly framed bikes more affordable to the public. The supplementation of a hi-tensile steel rear section helped keep the price down without adversely affecting performance.


Top tube: The top tube or cross-bar, connects the top of the head tube to the top of the seat tube.


Tuffs: Abbreviated term for Skyway Tuff Wheel mags. Is sometimes also used in a generic sense to refer to any mag style BMX wheel.


Two-pack paint: Two-pack Acrylic Enamel, Twin Pack, or ‘2K’ as it’s sometimes known, is a modern professional paint system which replaced the cellulose auto paints of old. Two-Pack paint consists of an acrylic and melamine resin which is mixed with a second resin, or hardener, called poly-isocyanate resin, creating chemical which begins the hardening process. Curing is accelerated by heat. A two-pack paint finish is hard wearing and often has a unique depth of colour.





U-brake: A form of cantilever brake that works like a centerpull caliper. The upside-down “L”-shaped arms cross over above the tire, so the left brake shoe is operated by the right side of the transverse cable. A U-brake uses studs that are above the rim, rather than below it, as with conventional cantilevers.





V-Brake ®: A Shimano trademark for a direct-pull cantilever brake, which does not use a separate transverse cable. A V-Brake has two tall arms, one of which has a housing stop and the other an anchor bolt. The exposed part of the cable runs horizontally from one arm to the other. V-Brakes and other direct-pull cantilevers have more mechanical advantage than other brakes, so they require special hand levers with less-than-average mechanical advantage to keep the overall mechanical advantage in a useful range.





Yoke: A fitting used on centerpull caliper and cantilever brakes which use a transverse cable. The yoke is the part that connects the main cable to the transverse cable. This is often misspelled as ‘yolk’.





Z-Mags: A composite 5 spoke mag wheel first manufactured in the early 80s, ACS Z-Mags are injection-molded with glass-filled nylon. Z-Mags are still manufactured by ACS today in black.


Z-Rims: A composite rim designed and manufactured by ACS using DuPont’s unique Zytel material with the goal to bridge the gap between light weight racing rims and the strength of freestyle composite mags.