Only the adjustable race and top/locknut from an ISO or JIS HS can be used.
The ITA thread is cut at a slightly different angle, but the steerer will recut the HS threads if the former is steel and the latter aluminium.
The OD of the frame cups and ID of the crown race are different though, so they still need to be ITA.
@Scilly.Suffolk started
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Only the adjustable race and top/locknut from an ISO or JIS HS can be used.
The ITA thread is cut at a slightly different angle, but the steerer will recut the HS threads if the former is steel and the latter aluminium.
The OD of the frame cups and ID of the crown race are different though, so they still need to be ITA.