here is a crazy question cant you just use a 12 point socket. casue asquare head will fit in it just the same . may not have as much mating surface as a 8 point but should work fine.

 

Is there a write up on doing the band adjustment anywhere?

 

A 12-point 5/16 socket is too small and a 12-point 3/8 is too big. Maybe a 12-point 11/32 socket would work if you could find one. I found a whole bunch of sears 8-point sockets on e-bay you can buy for about $10-12 including shipping.