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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.

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.

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.

Speed - the number of cogs at the back the chain was designed to be used with.

Compatibility - the brand and/or shifting system the chain is compatible with. Universal means the chain can be used with any standard shifting system, as long as the speed and width are correct.

Chain width - the gap between the inner plates where the chain sits on the sprockets. 3/32" has been standard for bikes with derailleur gears since the mid 1900s. When 9 speed was introduced the spacing reduced slightly but if the speed & compatibility are correct this isn't something you need to pay attention to. Single speed, track & BMX bikes will require either a 3/32" or 1/8" chain depending on the width of the rear sprocket and/or chainring. There's also a much wider 3/16" moped chain which can be used as a heavy duty chain for bikes without gears if required.

Chain pitch - the distance between the rollers (the cylindrical parts that roll around the pins). Pretty much every bicycle chain will be 1/2", the only time you will need a different pitch is for very early track bikes that take a 3/16" chain (also known as 'inch pitch'), or Shimano's short lived 10 mm pitch system from the 1970s/80s.

Number of links - the total number of links in the chain. If you're unsure how many links you need, you can measure your old chain (or a bike with a similar setup to yours).

Chainring count - the number of chainrings on the chainset. Fixed gear track bikes, single-speeds and some geared bikes use a single chainring, road bikes commonly use a double (two rings) and most touring bikes and mountain bikes will use a triple chainset (three rings).

Tooth count - the number of teeth on the chainring(s), the higher the number the harder the gear.

Chain width - this is only relevant for chainsets with a single chainring - if this is ⅛” then you must use a ⅛” chain. All double and triple (and some single) ring chainsets will use a standard 3/32” chain.

BCD - stands for Bolt Circle Diameter (sometimes referred to as PCD - Pitch Circle Diameter) and is only really needed when changing chainrings. To calculate the BCD, measure the distance in millimeters from the centre of any chainring bolt to the centre of an adjacent one and multiply it by 1.709 (you’ll likely need to round the resulting number up or down a little to get your BCD measurement).

*Intended speed - the number of cogs at the back the chainset was designed to be used with. We refer to it as ‘intended’ speed as most double and triple chainsets will actually work with different speeds than originally intended, but the further away you get from the intended speed the more likely you are to experience minor setup issues. The exception being some chainsets intended for 10 speed use or higher, with these it’s better to stick to the intended speed.

Crank length - this is measured from the absolute centre of the bottom bracket hole to the centre of the hole for the pedal.

Pedal threads - the pattern of the thread that your pedals screw into, this is usually stamped on the pedals themselves and most bikes use a standard thread of 9/16” x 20 tpi. The exceptions being older French bikes, bikes with cheaper one-piece type chainsets and Shimano’s Dyna Drive system (easily identifiable as the pedal holes are about an inch wide!).

Bottom bracket type - ‘square taper’, as the name suggests have a square shaped axle that slots into the chainset and ‘cottered’ axles are round and secured by pins - pretty much every bike up until the 1990s would use one of these, cottered being the much earlier system. Since then, different manufacturers have introduced their own systems that are not interchangeable so you must use a chainset that matches.