DT Swiss rear hub end cap kits convert your hub to fit a new axle measurement or for a new group set (HG vs XD).
These end caps do not convert non-Boost hubs to Boost 148mm spacing. DT 142x12mm and 148x12mm hubs simply share the same end caps.
They are also used for 12x157mm DT Swiss hubs, or to convert a 12x150mm hub to 157mm.
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