PTO attachments are universal for the speed of the PTO.
I would assume most of the tractors that get discussed on this forum has a 540RPM PTO. I would guess, but don't know it for fact that most cat 0 and cat 1 PTO attachments would be 540RPM. attachment
Yet when you start getting into the utility tractors and larger, they can be 750RPM or 1,000 RPM, which can require a different spindle on the PTO shaft.