Kyosho ball diff allen hex wrench
 

Since I like to have nice tools from my SnapOn stuff for building full-sized race chassis, all the way down to 1/43 scale. I have tried to ditch the L-wrenches everywhere possible. So I looked at the provided one with all of my Kyosho diffs and they measure out exactly at 1.25mm. What, 1 and 1/4 millimeters I've never heard of one. So my dNano buddy suggested [duh!] try SAE sizes. Voila!!! Good old American .050" is the ticket. Here is a pic of my trusty old Hudy driver that I use. Fit is a little tight but nice "feel" on torquing.