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Spoke Drilling - the number of holes for the spokes (front/rear), your wheel rims need to match the hubs exactly.

Spacing (O.L.D.) - the width of the hubs measured at their widest point, from the outside of the locking end nuts (O.L.D. = Over Locknut Dimension), not including the hub axle. These measurements need to match the inside of your frame and fork’s dropouts. Steel frames can be stretched or squeezed a few mm but it's always best to avoid this if possible, aluminium or carbon frames should never be stretched.

Speed - the number of cogs the rear hub was designed to be used with.

Sprocket Fitting - for cassette hubs this refers to the spline pattern (the shape of the cogs where they slide on to the hub) and this must match the cassette you intend to use. With freewheel hubs it refers to the thread, ISO is the modern standard and is almost exactly the same as older English/British and Italian thread, allowing you to mix and match between these thread types as long as it's not going to be under extreme force, in which case it's best to stick to an exact match. Freewheel hubs with a French thread must be used with a French threaded freewheel.

Spoke Drilling - the number of holes for the spokes (front/rear), your wheel rims need to match the hubs exactly.

Spacing (O.L.D.) - the width of the hubs measured at their widest point, from the outside of the locking end nuts (O.L.D. = Over Locknut Dimension), not including the hub axle. These measurements need to match the inside of your frame and fork’s dropouts. Steel frames can be stretched or squeezed a few mm but it's always best to avoid this if possible, aluminium or carbon frames should never be stretched.

Speed - the number of cogs the rear hub was designed to be used with.

Sprocket Fitting - for cassette hubs this refers to the spline pattern (the shape of the cogs where they slide on to the hub) and this must match the cassette you intend to use. With freewheel hubs it refers to the thread, ISO is the modern standard and is almost exactly the same as older English/British and Italian thread, allowing you to mix and match between these thread types as long as it's not going to be under extreme force, in which case it's best to stick to an exact match. Freewheel hubs with a French thread must be used with a French threaded freewheel.

Fixing Type - if you have small mounts on either side of the frame’s down tube you need braze-on shifters, if there are no mounts you’ll need clamp-on (sometimes referred to as band-on). Some 'aero' frames have mounts fixed to the top of the down tube, for these frames you require top mount shifters for the correct boss type (see below).

Shift Type - friction shifters don't click into gear when you change, when they do click it's referred to as indexed shifting. For this to work correctly you must use the same system as your rear derailleur, if you're using friction levers you can mix and match. You don't need to worry about the front derailleur as left downtube shifters aren't indexed.

Speed - the number of cogs at the back the right shifter is designed to be used with. This is important with indexed shifting but with friction shifters you can in theory run any shifters with any speed setup, although the right lever will need to be pulled back further to shift into the larger cogs.

Shifter Boss Type - the shape of the mount (for braze-on fixings only). Campagnolo / ISO is standard and easily identified by the flat sections on either side, usually combined with a square base for the backing stop plates to fit. There are also Shimano ones with a keyhole shaped base and much less common French ones that are round with no flat sections.

Boss Thread Size - M5 (5 mm) is standard for Campagnolo / ISO bosses, but Shimano bosses will often have M4.5 (4.5 mm) threads and the French bosses would likely have 5 x 1 mm threads.