Tutoriel to change your leather watchstrap with screw ties: Panerai, Cartier, Audemars Piguet Royal Oak Offshore...
Screw in pins.
Watches with screw in ties (video):
You can buy your watchmaker's screwdriver on that website.
1. Unscrew pin with a screwdriver appropriate (the second screwdriver might be needed for some watch models with 2 visible screws on each side of the watchcase). 2. Remove the screw ties system. 3. Place the new bracelet and re-screw the pin thru the new strap.