Metallics JMTLN5SS Nut M5 Hex Kep Lock Nut 18-8 SS (Jar 100)

The JMTLN5SS is an M5 metric hex kep nut, so it threads onto M5 screws and studs. It will not work on imperial threads like #10-24 or 1/4-20, even though those sit close to M5 in diameter. Metric and inch threads have different pitches and will cross-thread.

They are 18-8 stainless steel, the common austenitic 300 series grade, which resists rust in wet and outdoor environments far better than zinc-plated steel. The tradeoff with 18-8 is lower strength than a hardened alloy steel nut, so it suits general electrical and enclosure assembly rather than high-torque structural work.

A kep nut (also called a K-lock or washer nut) has a free-spinning external-tooth washer captive on its bearing face. The teeth bite into the mating surface as you tighten, which is what resists loosening from vibration, so no separate lock washer is needed. One part instead of two also means nothing to drop in a panel.

They ship 100 nuts to a jar, and the jar is the pack type, so you are buying the full count of 100 rather than loose pieces. The jar is the right form for a bench or van drawer where you are pulling a few at a time.

Expect some marring. The serrated washer face on a kep nut is designed to dig into the mating surface, which is how it locks, so it will score paint or powder coat under the nut. On a finished surface where appearance matters, use a plain hex nut with a flat washer instead and accept that you lose the vibration resistance.

Kep nuts are generally treated as single-use locking fasteners. Once the washer teeth have been set, the locking action drops off on reassembly, so for anything you expect to service repeatedly, a nylon insert lock nut or a plain nut with thread locker is the better choice. For one-time panel and bracket assembly, the 18-8 stainless kep nut is fine.

Stainless against aluminum is a dissimilar metal pairing, and in a wet or coastal location the aluminum is the one that corrodes. It is a common and accepted combination indoors and in dry runs; outdoors on aluminum, isolate with a nylon or coated washer, or use an aluminum compatible fastener.