Theres only 3 bits of info you need to order a new shock bush 1) the bushing which will either be 12.7mm (1/2″ in old money) or 12mm 2) the bolt size (either 6mm or 8mm) and then measure your existing bushing. So for instance for a Fox RP3 it’s 12.7 x 8mm x 22.0 or whatever. We list ours as either 6.1mm or 8.1mm bolt size at BETD as that’s just a clearance size for a 6 or 8mm bolt. It’s easy really.
There are odd ball sizes for some Santa Cruz or other frames and also old Rock Shox are 10mm bush size but these are old and rare now.