Ball sizes and leg levelers for EM games
Pinball machines take a 1 1/16" ball. Pitch and bat games use 7/8" balls before about 1960 and 3/4" from 1960 on (check the game). EMs take 2" leg levelers (3" are for later solid state games).
Systems
Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part One, Clay Harrell (pinrepair.com)