The Original Robertson square drive bit is the original and still best
fitting square drive bit. The 12 bit set includes:

1 - 1" x #0
1 - 1" x #1
2 - 1" x #2
1 - 2" x #1
2 - 2" x #2
1 - 2" x #3
1 - 3" x #1
2 - 3" x #2
1 - 3" x #3