Most 1" headsets have a 26.4mm crown race (except for some cheaper sets that may have 27.0mm). But that doesn't say that these are all compatible with the lower cups. Better be sure that you get the right brand & type.
@Dutch_Cheese started
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Most 1" headsets have a 26.4mm crown race (except for some cheaper sets that may have 27.0mm).
But that doesn't say that these are all compatible with the lower cups.
Better be sure that you get the right brand & type.