Chuck,
They are vinyl with a mild adhesive. Not so sticky that when you pull them off you damage the original paint but sticky enough that they stay.
The downside is they are not as detailed as the original. The center of the "A" on Tachymeter could be clearer and the small tick marks between the 90 and 110 could be better. BUT, considering the train wreck that I am covering, it is a BIG improvement. They are also soft, so don't bump them against the wall. :-P
This guy claims that he can make an identical insert to the original (metalized) but the tooling is significantly more. $100's of dollars for the setup and it would include about 20 bezel inserts. The rub is that I HAVE to have an original in order to get the exact size. If somebody would like to loan one in exchange for.................
dave