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Chainset Type - the number of chainrings the derailleur was designed to work with. ‘Double’ derailleurs are actually capable of working on ‘triple’ chainsets but they may struggle when shifting, especially if there’s a big step down from the middle to inner ring, so it’s better to match these correctly.

Frame Fixing - the way the derailleur fixes to the frame, if you have a tab on your frame to mount the derailleur to you need braze-on. If there’s no tab then you require a clamp-on type (also referred to as band-on or clip-on), these come in different sizes to match the diameter of your seat tube.

Pull Type - the direction of which the cable needs to ‘pull’ the mech in order to shift. If your cable runs up to the derailleur from the bottom bracket area then you need bottom pull, if your cable comes down from above you need top pull. Some later derailleurs can be used for either setups, these are referred to as dual pull.

Designated Speed (9 Speed & Above) - the speed of the chain that the mech was designed to be used with. This only becomes relevant for mechs marketed as 9 speed or above when chains became narrower, as the derailleur cage plates became marginally narrower too. We refer to it as ‘designated’ speed as technically you can use (almost) any derailleur with any chain, however if you want optimum performance it’s best to stay close to the manufacturers recommendations.

Indexing System (Shimano Only) - this is only applicable when using Shimano shifters that have an indexed left shifter such as STI or Rapidfire. For the indexing to work correctly when using these shifters the derailleur and shifters must be of the same type, so Shimano drop bar shifters need to be matched with a Shimano ‘road’ derailleur, and Shimano flat bar shifters must be used with Shimano ‘MTB’ derailleurs.

Chainset Type - the number of chainrings the derailleur was designed to work with. ‘Double’ derailleurs are actually capable of working on ‘triple’ chainsets but they may struggle when shifting, especially if there’s a big step down from the middle to inner ring, so it’s better to match these correctly.

Frame Fixing - the way the derailleur fixes to the frame, if you have a tab on your frame to mount the derailleur to you need braze-on. If there’s no tab then you require a clamp-on type (also referred to as band-on or clip-on), these come in different sizes to match the diameter of your seat tube.

Pull Type - the direction of which the cable needs to ‘pull’ the mech in order to shift. If your cable runs up to the derailleur from the bottom bracket area then you need bottom pull, if your cable comes down from above you need top pull. Some later derailleurs can be used for either setups, these are referred to as dual pull.

Designated Speed (9 Speed & Above) - the speed of the chain that the mech was designed to be used with. This only becomes relevant for mechs marketed as 9 speed or above when chains became narrower, as the derailleur cage plates became marginally narrower too. We refer to it as ‘designated’ speed as technically you can use (almost) any derailleur with any chain, however if you want optimum performance it’s best to stay close to the manufacturers recommendations.

Indexing System (Shimano Only) - this is only applicable when using Shimano shifters that have an indexed left shifter such as STI or Rapidfire. For the indexing to work correctly when using these shifters the derailleur and shifters must be of the same type, so Shimano drop bar shifters need to be matched with a Shimano ‘road’ derailleur, and Shimano flat bar shifters must be used with Shimano ‘MTB’ derailleurs.

Tooth Count - the number of teeth on the chainring, the higher the number the harder the gear.

Between Adjacent Bolt Holes - the measurement from the centre of any bolt hole to the centre of an adjacent one, if this measurement is the same as that of your crankset and the bolt count is the same then the chainring should fit.

BCD - stands for Bolt Circle Diameter (sometimes referred to as PCD - Pitch Circle Diameter) and is the technical way to determine whether the chainring fits your crankset. To calculate, multiply the distance between adjacent holes (in mm) by 1.709 (you’ll likely need to round the resulting number up or down a little).

Bolt Count - the number of bolts securing the chainring to the chainset. As with the BCD, this must be the same as your chainset.

Chain Width - 3/32” is the standard width for double and triple chainsets, wherease 1/8” chainrings are only found on single ring chainsets, generally for track / singlespeed use and can only be used with a wide 1/8" chain.

Intended Speed - the number of cogs at the back the chainring 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 chainrings intended for 10 speed use or higher, with these it’s better to stick to the intended speed.

Tooth Count - the number of teeth on the chainring, the higher the number the harder the gear.

Between Adjacent Bolt Holes - the measurement from the centre of any bolt hole to the centre of an adjacent one, if this measurement is the same as that of your crankset and the bolt count is the same then the chainring should fit.

BCD - stands for Bolt Circle Diameter (sometimes referred to as PCD - Pitch Circle Diameter) and is the technical way to determine whether the chainring fits your crankset. To calculate, multiply the distance between adjacent holes (in mm) by 1.709 (you’ll likely need to round the resulting number up or down a little).

Bolt Count - the number of bolts securing the chainring to the chainset. As with the BCD, this must be the same as your chainset.

Chain Width - 3/32” is the standard width for double and triple chainsets, wherease 1/8” chainrings are only found on single ring chainsets, generally for track / singlespeed use and can only be used with a wide 1/8" chain.

Intended Speed - the number of cogs at the back the chainring 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 chainrings intended for 10 speed use or higher, with these it’s better to stick to the intended speed.

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 setups you can in theory run any shifters with any speed setup.

Shift System - 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 shift system as your rear derailleur.

Shifter Type - brifters' are designed to be used on road drop type handlebars and 'trigger' shifters are designed to be used on flat bars, usually for mountain bikes.

Chainset Compatibility - the number of rings on the chainset the left shifter is capable of working with (providing the front derailleur is capable of the same).

Brake Type - if you’re running direct pull cantilevers (V-Brakes), you’ll need compatible shift/brake levers. For traditional side pull calipers, cantilevers and mini V-brakes you’ll need shift/brake levers designed to be used with these as the cable pull is different.