A long time ago, my father worked in a head shop in the late 60s early 70s. He did custom leather work, vests, bags, various adornments, etc. His old leather-working tools are still in that basement, and I have picked up a little of the craft. Here is an ible on how to make a custom wrist cuff.
Leather (3"x9-10", at least 2mm thick)
hole punch (any awl will do in a pinch, but a leather hole punch is ideal)
leather rivet and snap setting kit
small leather rivets
The first step is to decide the circumference, measure your wrist and decide how much slack you want.
Mark with a pencil on the leather where you want to cut. Using razor blade, cut along a straight-edge until you have the desired shape and size.
Step 1: Holes!
Line up a ruler with the marks for the snaps (I had already done the snaps in the photo) and mark approximately 3/4 inch intervals for even spacing.
Use your hole-punch to make holes slightly larger than the rivet studs. Repeat on the other side.
Step 2: Snaps
Next place the snap mouth on the correct sized snap setting bump on the rivet setting plate, place appropriate hole over it and then snap cap. Use a concave setting punch so as not to deform the cap, and set the snap using 3-4 good blows with the mallet be careful not to deform the mouth of the snap as it will not fit and you will have to replace it. If mistakes are made in either the snap setting or rivet setting use end-cutters to remove offending rivet and replace with new one. Be sure to put the snaps in properly, you want both the caps and mouths on one end and the studs and tongues on the other end, as you want the tongue on the face, and the cap on the face.
Step 3: Rivets
First put the stud on the plate as before, next put the leather with the right hole over it and place the cap on. As before, a few solid blows should set it properly. Use the same concave setting punch. If it seems stuck wiggle it, or pry off with screw-driver or pliers, try not to rip out the rivet getting it off.
Repeat this process until all the holes for the rivets are filled.