I thought you could use Hollowtech BBs with GXP?
What I must be thinking of is the On-One outboard bearing track chainset, which came with a rubbish BB but was compatible with Hollowtech.
There are adapter bushings which convert some 24mm NDS bearings to the 22mm required for GXP, but they're a bit pointless when native GXP BBs are easy to find.
Could you be thinking about the FSA chainset which are also 24mm?
@tbc started
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I thought you could use Hollowtech BBs with GXP?
What I must be thinking of is the On-One outboard bearing track chainset, which came with a rubbish BB but was compatible with Hollowtech.