@thor cats can push through any opening wide enough to fit their head, neck is thinner. Collars generally need to be clamped on neck, not pulled onto head since that would mean they can also be taken off by pulling the other way.
@Amikke the collar uses a strap. the instructions i found tell you to assemble the collar first. it takes a few minutes to do it. it's one of these collars:
@Amikke ironically, i asked for a cat collar. came home. it says dog collar on it. but for small dogs.