There to be other drive sizes years ago. Now we have the survivors 1/4, 3/8, 1/2, 3/4, 1 , 1-1/2. I have a number of Plomb and Snap-On 9/32 sockets and drive tools from the 1940s. I have a modern Proto socket in 5/8 drive. I am surprised someone hasn't come up with a drive size in metric. 8mm, 12mm, 14mm, 18mm ?
EvilDr235