Each tape carries a row of teeth spaced one pitch apart, but the two rows are offset from each other by half a pitch — so a tooth on the left tape always lines up with the gap between two teeth on the right tape, never with a tooth head-on.
The slider's body is a Y-shaped channel: on the open side it has two separate grooves, one for each tape, that taper together toward a single point — the mouth. A thin wedge (the "blade" or separator pin) sits exactly at that point, riding between the two rows.
- Pulling the slider toward the closed side makes each tape ride along the narrowing wall of its groove, camming it sideways toward the centreline as the groove tapers.
- Because the rows are offset by half a pitch, the teeth don't collide as they're pushed together — each tooth's tip slots past the centreline into the space between its neighbours on the opposite row, hooking together.
- Pulling the other way runs the already-interlocked teeth back over the wedge tip, which physically pries the alternating teeth apart before the diverging grooves guide each row back out to its own side.
- The slider itself does no gripping — it only bends the two flexible tapes through a fixed funnel shape, exactly like the 3D zipper-mechanism model but viewed as a flattened, top-down cross-section.