Metallics JMTLN12SS Nut M12 Hex Kep Lock Nut 18-8 SS (Jar 100)

It's an M12 metric hex Kep nut, so it threads onto M12 bolts, studs, or all-thread. Metric only, it won't run onto a 1/2 inch UNC stud even though the two diameters look close.

The nut is 18-8 stainless steel, the common 300 series austenitic grade used for general corrosion resistance. That makes it suitable for damp and outdoor work such as exterior strut, enclosure mounting, and grounding hardware. For salt spray or pool chemical exposure, 316 stainless is the usual step up.

The free-spinning star washer is already attached to the flange of the Kep nut, so you don't add a separate external tooth washer. Run the nut down and the washer teeth bite the mounting surface as you torque it, which is why electricians use them on strut, panel, and enclosure hardware where vibration can back a plain nut off.

Mechanically it tightens fine on paint, and the washer teeth will cut through coating as they seat. But do not rely on a Kep nut alone as the bonding path on a painted or powder coated enclosure. Where a listed ground connection is required, scrape the paint or use a listed bonding washer or grounding screw rated for the job.

Both resist back-off, but they do it differently. The Kep nut locks against the mounting surface with its toothed washer, so it works where the nut seats on sheet metal or strut and you want a one-piece install. A nylon insert nut locks on the thread itself, so it holds on a through-stud where the nut doesn't bear on a face, but the nylon limits service temperature. For hot locations or where you want surface grip, the 18-8 stainless Kep nut is the one.

100 nuts per jar, and the jar pack is what you buy, there is a single model, JMTLN12SS. The jar is handy on a service truck since it reseals and keeps loose metric nuts from mixing with your inch hardware.

Once the washer teeth have bitten into the surface the locking action is reduced, so for anything that carries vibration or a safety load, fit a fresh nut on reassembly. At 100 per jar, replacing them on teardown is cheap insurance. The nut body itself is 18-8 stainless and won't gall the way a plated steel nut can.