Most Pachinko machines take two pieces of glass for the playing field covers. This is so people can't use magnets to cheat at the game. The inside cover is a 1/8" plate glass (This is for sound insulation and to keep the balls on the playing field), and the outside cover is 1/8" Plexiglas (This is to absorb shock and for protection). There are two grooves in the metal frame around the plaing field to hold the glass in place.
Here are some of the most common machines glass sizes.
Nishijin Single Shoot glass size is 15.9"X20.0"
Nishijin Model-A glass size is 15.9"X17.9"
Nishijin Model-B glass size is 15.9"X16.0"
Nishijin Model_C glass size is 16.0"X16.0"
Sankyo glass size is 16.0"X15.4"
Sanyo glass size is 16.0"X15.4"