A turn lock is the classic closure for a handmade bag flap: a slotted plate on the flap, a pronged base on the bag body, and a satisfying click when the two meet. Most ruined installations come from the same three causes — the two halves misaligned, slots cut oversize, or leather too soft to hold the prongs. This guide walks through a clean installation. If you are still choosing a lock, start with purse lock types explained and the purse lock size and screw spacing guide; ready-to-install locks are in the bag locks and clasps collection.
Before You Cut: Anatomy of a Turn Lock
A standard turn lock has four parts: the turn button and front plate (visible on the flap), the backing plate that sandwiches the flap leather against it, the base plate with the slot the button turns into, and the prongs or screws that clamp everything together. Prong-backed locks suit most leatherwork; screw-backed versions suit thicker builds and can be disassembled later. Check which type yours is before cutting — the slot layout differs.
Step 1: Mark the Two Halves from the Finished Bag
Assemble the bag body and flap completely first — never position a lock on flat pattern pieces. Close the flap where it will sit in use, with the bag filled to a realistic load. Mark the center of the flap edge, then mark where the button will sit on the flap and where the slot must land on the bag body. The slot position is fixed by the flap: hold the flap's finished edge in place and transfer the mark straight down. A lock installed 2 mm off-center will twist the flap every time it closes.
Step 2: Reinforce the Leather
Turn locks concentrate force on a few square millimeters of leather. On chrome-tanned leather under about 1.4 mm, glue a reinforcement patch (a circle of firm leather or salpa board, slightly larger than the plate) inside the flap and behind the base plate position on the bag body. Skive the patch edges so it disappears. Vegetable-tanned leather at 1.6 mm or more usually needs no patch.
Step 3: Cut the Slots
Trace the plate's openings onto the leather — the button slot on the flap, the prong slots (or screw holes) on both pieces. Cut slots with a sharp craft knife or slot punch, slightly undersize: leather stretches, and a slot cut too big leaves a gap around the plate that no amount of pressing will hide. Test-fit the parts, and only then enlarge in small passes until the prongs pass through snugly.
Step 4: Set the Flap Half
Push the button stem through the flap slot from the front, place the backing plate over the prongs on the inside, and bend the prongs — outward along the plate's channels, not straight down into the leather. Press them flat with pliers; a prong tip left standing will print through the flap or scratch the bag's contents. On thin leather, put a scrap pad under the prongs before bending so the leather compresses, not stretches.
Step 5: Set the Body Half and Test
Repeat for the base plate on the bag body. Close the flap, insert the button into the slot, and turn. The action should be firm but smooth — if it grinds, the two halves are misaligned; if it is loose, the leather stack is too thin for the lock (add a shim behind the backing plate). Open and close twenty times and check that no prong has shifted.
Common Mistakes
- Marking before assembly — the flap never lands where the flat pattern promised; always position from the assembled bag
- Slots cut to finished size immediately — cut small, test-fit, enlarge; you cannot uncut leather
- No reinforcement on soft leather — the prongs tear through within weeks of daily use
- Prongs hammered flat against the table — this dents the front plate; bend prongs with pliers, supported from the front
The same sandwich-and-prong logic applies to twist clasps and tuck locks. Browse sizes and finishes in the bag locks and clasps collection, and for the other fittings around the closure — rings, rivets, chains — see our bag hardware buying guide and the tutorial on installing double cap rivets.