Prepare a piece of leather with a thickness of about 2.5 mm that has a circular hole with a diameter of about 2.5 cm and a slit of about 2 cm.
Here we use a kit product "Plastic Bottle Holder Kit" from LeatherCraftTools.com.

Finish the edge and flesh side which become a loop by folding back.

Roughen the surface to be glued with an abrasive stick or the like.

Put the metal fittings on the leather.

Apply a bond to one side of the gluing surface, fold the leather and attach it carefully.

Use Leather Craft Roller, Hand Crimper Wide, etc. to crimp firmly.

Finishing the edges with a finishing agent will make it look better.

Sew the perimeter of the attached surface.
Because this part of the leather can easily peel off with use, sew both sides of the slit for reinforcement.

This sample was sewn using VINYMO <MBT> Polyester Machine Thread (thickness: # 5, color: 171).

Complete.

Example use.