if it's not at least 25.4mm it's back to square one.
It only needs to be over 22.2mm ID to get a quill for a 1" steerer up there, anything over that can be shimmed.
But I haven't yet seen a quill adaptor that isn't at least 25.4 where the stem clamps
Ah, you're thinking of stuffing it right up there. I thought you might just cut the bottom off to use the ready made wedge and add an appropriate screw and washer to tighten it.
@TvH started
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It only needs to be over 22.2mm ID to get a quill for a 1" steerer up there, anything over that can be shimmed.