I just picked up an old socket set - and there are these weird sizes included. Upon further research, I found that these sizes were used in the earlier automotive and manufacturing industries. Early GM manifold bolts are 19/32" for proper fit. Model A Fords used a 21/32" for various rear differential components. These are common sizes for early auto restorations - possibly even motorcycle related components? Upon further inspection they are quite similar to 1920s Snap-On sockets with the knurling around the socket and no logo. Now I just need the 5 Window to go with 'em . . .