My chin rest came.

The problem is, it came with a key.

As a native tinkerer, I’m torn between, “Let’s see if I can’t change it myself,” and “You will screw it up and necessitate a trip to the music store to fix it, so just go there straight off.” Besides, I think the threads on my current chinrest are stripped, so I’m loathe to take it off for fear that if I can’t get the new one on, I won’t be able to put the old one back.