This is the set of adapters for Crown ring bolts, which allows you to use M12 bolts with 14 mm holes on the Carrier unit. For example, all ///M differentials have 14 mm holes, so you can swap the gear ratio from another differential which has M12 bolts, using these adapters.
The most often gear ratio swap is in E46 M3 differential. Everyone who is running N/A S54B32 engine is chasing shorter ratios. Aftermarket Gear ratio sets are very expensive. You can find 3.91 gear ratio that can be used from E32 and E31. But crown gear has M12 bolt holes and E46 M3 LSD unit has holes for M14 bolts. In this situation, you put these sleeves in Fi 14mm holes to use M12 bolts.
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