This type of sight was used on the 6″ Colt Diamondback, and was installed in a factory cut slot in the barrel. These are original Colt mfg replacement sights, and since the hole location can vary they need to be drilled for the pin. The hole in the barrel rib is 1/16″, so the sights can be drilled with a standard 1/16″ drill bit available in most hardware stores.

To avoid enlarging the hole in the barrel rib, we would recommend that you don’t drill with the sight installed in the slot. It’s safer to put the sight in the slot and only drill enough to make a dimple in the sight, then take it out of the slot and drill it separately.