Metallics JLWI12 Washers 12 Int Tooth Lock St-zn (Jar 100)

The JLWI12 is a #12 internal tooth lock washer, so it is sized for #12 machine screws and sheet metal screws. Internal tooth washers put the teeth on the inside diameter, biting the screw head seat rather than the surface under the washer, which is why they are used where you do not want tool marks on a finished panel or cover plate.

Each jar holds 100 of the #12 internal tooth lock washers. The jar pack is the standard way these move for service trucks and panel shops, since it keeps small fasteners from scattering in a parts bin.

They are zinc plated steel. That handles dry indoor electrical work, panel assembly, device boxes, and enclosure covers. For wet, outdoor, or corrosive locations, step up to stainless steel instead; zinc plating will eventually sacrifice and the washer will rust.

Internal tooth, like the JLWI12, spreads its grip over many small teeth inside the bore and keeps the bearing face smooth, so it is the choice on painted covers, thin sheet metal, and anywhere the finish shows. A split ring concentrates all its load on two cut ends and will gouge a soft or finished surface, but it gives more spring travel on thicker steel. For electrical panel and device work, the internal tooth is the usual spec.

The JLWI12 is built to ANSI dimensional sizing, which is what lets it interchange with any other #12 internal tooth lock washer already on the job. That matters for MRO and institutional buyers standardizing a fastener crib across multiple buildings.

Treat them as single use. The teeth on the JLWI12 deform into the screw head seat on first tightening, and once flattened they no longer provide the spring load that keeps the screw from backing out under vibration. Buying by the 100 count jar is cheaper than chasing loose screws, so replace them when you reassemble.