Just seen this man I just got done slinging mine back together yesterday. They are coarse thread and should be metric. Lots of people use a 5/8" wrench on them but 16mm is correct too. I know it's close to 7/16" bolt diameter but why would the t case shifter bolts be the only SAE fastener in the whole setup? They are metric to best of my knowledge. Actually come to think of it, they're the same size/thread/pitch as the bolts that fasten the front driveshaft to the t case output flange.