About alloy spacers: These high quality alloy crank spacers allow you to correctly align any compatible crank set in any frame bb shell, especially those in the new generation of asymmetric frames. Replacement spacers work with both Road and MTB bikes.
5mm+10mm spacers for long spindle "386Evo" format crank fitted to BB30A and PF30A (73mm asymmetrical bb's).
10mm is for Cervelo BBRight drive side only. There is no need for a spacer on the non-drive side.
If you are fitting a long spindle "386Evo" format crank on a BB30 or PF30 road (68mm) system, you will need two 10mm spacers, one on each side.
2.5mm spacers are for THREADED BB's ONLY, and are for spacing the bb cups outboard to correct chain line and fit specific cranks.