This is the default Fender Jaguar Special HH strap button which I dislike. It features the 'cup' design which serves to expand the strap slit over time.
Replaced it with a Planet Waves version with an additional felt inserted between the guitar body & the button itself.
It's not quite visible from the previous pic but here it is before going into the body. The benefit of having this in there is that it prevents the body finish from fusing with the button. This would prove damaging when you decide to unscrew deteriorated strap buttons for replacement; the button would lift off the finish & you'd hear this awful cracking sound only to realize the affected surface had indeed cracked.