Howdy, Pards,
I use Stewart's No. 150 Waxed Polyester thread (Coarse) for hand stitching (with a Speedy Stitcher*) the main seams of holsters and for sewing on buckle and tongue billets, etc. on belts. For other things, such as cartridge loops on belts I use #207 Nylon thread on my Juki TSC 441 machine (basic machine Ferdco Super Bull), and #277 Nylon thread for sewing on holster belt loops, etc. This stuff is unwaxed, but I run the thread wound on the bobbins through a cold wax bath as it is being wound on the bobbin.
*Note: For lighter stuff, I might use Stewart's #170 Fine Waxed Polyester thread in the Speedy Stitcher. With the #150, I use a Landis machine hook needle (the eye in the point has the one side open), in a Speedy Stitcher handle. With the Landis hook, I pre-drill the holes or punch them on the Juki with a needle and no thread, then push the hook through the holes, grab a loop, pull it back through the holes and push the other end of the thread through the loop thus formed. You could also do "double needle" stitching with the hook...if you are careful not to catch the first thread through the hole.