Quoted from Otaku:Should just be the standard size - 21" x 43" x 3/16" Tempered.
Make sure you tell them to not print the little text in the corner of it. I forget what it's called, but there is a name for getting it done that way and they WILL print the text on it by default. (It says "Tempered", etc., etc.)
Also, make sure they're not charging you an arm and a leg.
Not a good idea to leave that off. Anyone should know it's tempered glass. You put that up in the upper corners and nobody will ever see it anyway.
The glass size should be that size, but I just restored a Hot Line and I got a surprise in doing so. I replaced the plastic glass guides that go under the side rails with the part that PBR has available (545-5017-00). I've used those guides with no problems on Gottlieb games. On this game, after installation, a standard sized 21 inch wide glass was not wide enough, and it fell out of the guides. I ended up having to have a glass made that was 21.25" wide and it fit perfectly. It appears that the guides PBR sells under that part number are just a bit narrower than the original part.
If you aren't replacing the plastic guides a standard glass will work. The glass shop will tell you, though, that it is a good idea to leave the notice on there that the glass is tempered.