Metallics JMLWI3 Washers M3 Int Tooth Lock St-zn (Jar 100)

The JMLWI3 is an M3 internal tooth lock washer, so it goes on M3 metric screws and bolts. If your hardware is #4-40 or #6-32 imperial thread, this is not the right washer, you want an imperial-sized internal tooth lock washer instead.

An internal tooth washer like the JMLWI3 has its serrations on the inside diameter, so the teeth bite the screw and the clamped surface while the outer rim stays smooth. That keeps the teeth hidden under the screw head and avoids marring a visible panel or finished cover plate, which is why it gets used on device plates and enclosure covers. External tooth washers put the teeth on the outside for more bite area under a large head, and a split ring washer relies on spring tension at a single gap rather than serrations. All three are lock washers; the JMLWI3 is specifically the internal tooth style.

Yes. The JMLWI3 washers are zinc plated steel, which gives basic corrosion protection for dry interior work such as panel builds, enclosure covers, and device mounting. Zinc plating is not a marine or sustained outdoor-wet finish; for washdown or exterior exposure, step up to stainless.

Each jar holds 100 M3 internal tooth lock washers. Packed as a jar rather than a bag, so it stands up on a shelf or in a van bin without spilling, and the whole jar weighs 0.07 lbs, which tells you how small these washers are individually.

That is what it is built for. The serrations on the inside diameter dig into the screw head and the mating surface, which resists loosening from vibration on things like panel-mounted devices, motor covers, and control enclosures. Serrated lock washers work by biting into the material, so they do leave witness marks on soft or painted surfaces and are generally treated as single-use once the teeth are flattened.

The jar measures 3 x 3 x 2.15 inches, so it drops into a standard small-parts bin or a van drawer without a problem. Useful to know if you are standardizing a hardware station and stocking several thread sizes side by side.

The JMLWI3 M3 internal tooth lock washers are manufactured in China. Worth knowing if you are filling a job with domestic-sourcing requirements on the submittal.