A cycling glossary

4130	See Chromoly
Air-hardening steel	A type of steel that does not require quenching in water or oil to gain maximum strength. A frame that was tempered by quenching would likely warp or distort, and a non-hardening steel would lose some strength in the heated area.
Bottle boss	A threaded hole, usually found in pairs, in the down tube or seat tube of a bicycle, that allows the bolting-on of a water bottle cage. Some expedition bikes feature bottle bosses on the fork legs as well. Also called bottle braze-ons.
Braze-on	A generic term encompassing all permanent frame attachments except the tubes and lugs themselves. Examples include permanent cable guides, bottle bosses, and pump pegs. On welded bikes, braze-ons may be attached by welding, even though nobody calls them weld-ons.
Bronze-brazing	When applied in a molten state to hot tubing, bronze bonds to the steel and makes a sort of metallic hot glue. Molten bronze is a thick, gooey liquid that fills gaps effectively and makes a strong joint. It can be used in conjunction with lugs, or in lugless, fillet-brazed construction. Its melting point is 1600-1850º F.
Butting	The process by which a frame tube is manufactured to have thicker walls at the ends than in the middle. Butting compensates for loss of strength in some metals in the brazing process. Double-butted tubing has thicker sections on both ends, single-butted on one end. Seat tubes are typically single-butted. Triple-butted tubing is thicker on one end than the other. The difference in thickness is usually quite small, around 0.4mm, and is not detectable from the outside. Tubing without butts is called straight gauge.
Center-pull brakes	An archaic form of rim brake that uses long arms that arch back over the top of the tire, and a straddle cable for actuation. Center-pull brakes may mount on a U-shaped plate that attaches to the frame through holes in the seatstay bridge and fork crown, or with brazed-on studs like a cantilever or V-brake. Center-pulls are finding a new popularity as randonneuring grows, because they provide good modulation, stopping power, and the ability to clear wide tires and fenders. Need illustration
Chain hanger	A short peg attached to the drive-side seatstay, facing the wheel, about 8 inches above the dropout. Hang the chain on it before removing the rear wheel, and it'll be that much easier to get the chain back on the cog when it's time to put the wheel back on.
Chain rest	Similar to a chain hanger, but even simpler; a chain rest is a phantom cog, attached to the drive-side dropout. If the rider had a rear flat, he would shift the chain onto the chain rest, using the derailleur, before coming to a stop. The chain remains on the rest, without drooping, while the wheel is removed, and on starting again, the rider pushes off with one foot and immediately shifts the chain onto the appropriate cog.
Chromoly (also “chrome-moly”)	A high-strength alloy of steel composed of iron with small amounts of carbon, chromium, and molybdenum. Also called 4130, or by brand names such as Columbus, True Temper, or Deddaciai
Constructeur	A bicycle builder who goes beyond merely designing the frame and joining the tubes together to create a bicycle as a seamless whole, integrating lighting, racks and fenders into the total design. Most constructeurs build luggage racks specific to the bicycle, as well as handlebar stems. Lighting wires will be concealed inside frame tubes, as will control cables. A few constructeurs, such as Rene Herse in the ‘50s and Tony Pereira in the modern age, make their own derailleurs. Constucteur bicycles tend to be lighter than the factory-made equivalent, due to the lack of clamps; also stronger, and more free of rattles.
Crown	The top part of the fork. A fork crown may be a casting or a forging, with sockets that the legs socket into, or built up out of short pieces of tubing into what is called a segmented crown or a box crown. A fork in which the blades curve at the top to meet the steerer tube is called a unicrown fork.
Demountable	As Europe rebuilt the demolition wrought by World War II, more people bought cars and abandoned cycling. In an effort to lure them back, constructeur Rene Herse introduced a bicycle that separated into two sections, to travel in the trunk of an automobile. The conversion was effected by cutting a conventional frame in half, about four inches in front of the seat tube, and brazing a slightly smaller diameter tube into the stub. A pair of quick-release seatpost bolts at each joint held it together. To simplify cable routing, a pair of downtube shifters were brazed to the seat lug, so shifting gears made the rider look as though he were scratching a very personal itch. The term can also mean any part that disassembles or is removable.
Dropout	The place where the wheel axle attaches to the frame. Some builders favor dropouts (sometimes called “drops” for short) made from stainless steel or other very hard metals for durability. Others favor more ductile metals like mild steel, on the theory that a small, highly stressed part should have a little “give” in it for durability. Strictly speaking, it’s called a dropout if its shape allows the rear wheel to be removed without having to manipulate the chain. Hence, true dropouts open to the front of the bike or straight down, and only on the rear wheel. If they open to the rear, or are located on the front of the bike, they're properly called fork ends. No one else knows this but me (and you, now), and probably only one of us cares.
Fillet-brazing	Sometimes called lugless construction. A concave bead of bronze covers the joint of the tubes which, when painted, gives the joint a smooth and seamless appearance. Fillet-brazing allows the builder to join the tubes at angles for which lugs are not manufactured. Fillet-brazing requires more filing and sanding than lugged construction. Most builders charge a premium for fillet-brazing. Also erroneously called bronze-welding.
Generator hub/dynamo	A wheel hub, usually on the front, that contains a device for generating electricity to power a headlight and taillight. Some constructeurs add a USB socket so that the rider can charge a cell phone or GPS unit while riding, although most dynamos cannot do so while the lights are illuminated. Dynamos of all types, whether located inside the wheel hub or driven by the sidewall or tread of a tire, cause some drag and slow the rider slightly. In very long distance events, sometimes riders who generate their own lighting electricity receive a small handicap over riders with battery-powered lights.
Lug	A sleeve that reinforces the joint between two tubes. Lugs superficially resemble the fittings used to join plumbing pipes. Lugs may be stamped from sheet metal, cast, forged, or shop-made, from either steel or stainless steel.
Manganese-molybdenum	A high-strength alloy of steel composed of iron, carbon, manganese, and molybdenum. The common brand is Reynolds 531, ubiquitous in the classic era and rarely seen today. Manganese-molybdenum steels lose significant strength when welded, unlike chromoly, but can be bronze- or silver-brazed.
Mixte	A type of bicycle frame that combines a low stepover, like a ladies' frame, with the more robust construction of a men's frame. Mixtes dispense with a conventional top tube and instead use a pair of small tubes, similar to seatstays, that run from the head tube directly to the rear dropout. Originally intended as a unisex design, mixtes in the U.S. are seen as women's bikes, although this is less true in Asia and Switzerland. Some mixtes use a conventional diameter top tube from the head tube to the seat tube, and a second set of seatstays. Building such a mixte is one of the more complicated framebuilding tasks, and is rarely seen on production bikes.
Points	The portion of the lug that covers the tube may be longer on top and bottom than on the sides, to give the frame greater weight-carrying strength, without adding unnecessary lateral stiffness. Lug points often have a decorative function, and may be carved into graceful curves without having an engineering purpose. Need pic
Porteur	A flat carrier rack located over the front wheel, with a wide sturdy platform. The classic porteur rack is able to carry 110lbs. of newspapers, stacked flat. Modern iterations are much less hardily built, but still capable of toting large pizzas or a 12-pack. The term may also refer to a bicycle equipped with such a rack.
Pump peg	A small metal bracket allowing a tire pump to be carried on the bicycle's frame. Pump pegs can appear on the seat tube (either in front of or behind), top tube, or occasionally on the seatstay. The peg may be elaborate or as simple as a ball bearing stuck to the head tube with a drop of bronze.
Randonneur	A bicycle designed for long-distance, self-supported, non-competitive rides. Randonneuring rides have a time limit and perhaps accolades for the day's fastest rider, but no losers and no prizes. Common “rando” distances include 200, 300, 400, 600 and 1000 kilometers. A rider who completes all common distances in a single year is called a super randonneur.
Stainless	Short for stainless steel; a high-strength alloy of steel composed of iron, with large proportions of nickel and chromium, noted for its hardness and resistance to corrosion. Stainless steels brands include KVA, Reynolds 953, and Columbus XCR.
S&S couplers	Machined stainless steel couplings that allow a normal-sized frame to separate into two pieces. With the frame separated and the wheels removed, the bike should fit into a 26” by 26” by 10” suitcase, and can travel on an airliner without incurring punitive charges. A pair of couplers adds half a pound and about $800 to a frame. They can be added to existing bicycles by a competent framebuilder, although, since brazing is involved, a repaint is required. Some builders use a single coupler on the chainstay to allow a drive belt to be installed. A few builders have made triplets that convert to tandems by means of S&S couplers, and also tandems that fit into standard suitcases. S&S is a brand of Sands Machine Company. Tom Ritchey makes separating frames with its own BreakAway system, and Rene Herse built a number of demountables. In all cases, the frame couplings are located in the down tube and top tube, immediately in front of the seat tube.
Seat mast	An extended seat tube that extends above the top tube, nearly to the height of the saddle. On frames with large stand-over clearance, the builder may choose to extend the seat tube into a mast to avoid the use of an excessively long seat post. A seat mast will be less likely to bend than a seat post, because the rigidity of a tube, all else being equal, increases by the fourth power of its diameter. A frame with a seat mast will offer comparatively little seat height adjustment. This is less important on a custom, handbuilt frame than it would be on a production bike.
Shoreline	The edge of the lug that extends over the tube. Lug shorelines may be cut into fanciful or decorative shapes, but should never make a straight, circumferential line.
Silver-brazing	Usually used in conjunction with lugs, silver brazing is a method of joining frame tubes with a metallic “hot glue.” Different silver brazing compounds have differing silver content, ranging from almost none to almost pure. Silver brazing utilizes lower temperatures, (around 1200-1300º F) than bronze-brazing, important when working with certain tempered steels, like Reynolds 753. While quite strong, silver doesn't fill gaps well, so most silver brazed frames use bronze-brazing at the dropouts and fork ends. Also erroneously called silver-soldering.
Straight-gauge	Tubing without butts, of a consistent wall thickness throughout its length.
Tang	Not the beverage of astronauts, a tang is a triangular reinforcement extending from a fork crown down the blade, to increase side-to-side rigidity. Most builders place tangs on the side of the fork blade facing the wheel. Some fork crowns include tangs from the factory; others allow the builder to add them as he sees fit.
TIG-welding	Short for Tungsten Inert Gas welding. A method of joining tubes by which an electric arc, carried by a tungsten electrode resembling a nail, melts the metal of the tubes and allows it to flow together. An inert gas such as argon floods the area around the arc, protecting the hot metal from the oxidizing effects of oxygen in the air. TIG-welded joints have the appearance of a stack of tiny coins or fish scales, although they may be ground smooth, or smoothed by running over them a second time with the electric arc, a technique called second-pass or double-passing.
Thinning	The points of lugs are filed so that their thickness tapers over their length. This prevents the lug from creating a point of high stress on the tube that might, over time, act as a can opener on the thin metal of the tube. Gracefully thinned lugs are seen as a sign of craftsmanship. Most factory frames exhibit little or no lug thinning. http://www.bicycletimesmag.com/glossary