MS21042 Jet Nuts, All-Metal Self-Locking, Mil-Spec, 6-Point, SAE UNF (Choose Thread Size)

MS21042 all-metal self-locking jet nut (K-nut)

The MS21042 is an all-metal, self-locking nut made to military specification — commonly called a jet nut or K-nut. There is no nylon insert; the locking action comes from a slightly deformed hex, so the nut is temperature tolerant and holds torque where a nylon nut would fail. It is rated to 160,000 psi tensile strength and temperatures up to 450°F.

Two features make it a favorite on race cars, robotics, aircraft, and drones. Its hex is reduced compared with a standard nut, so it fits and can be tightened in tight spaces where a normal wrench will not swing. And it is considerably lighter than an equivalent nylon-insert lock nut — replacing a car’s worth of nylon lock nuts with jet nuts is a real, if small, weight saving.

These are supplied as plated steel with SAE (fractional inch) UNF fine threads only. Choose your thread size from the drop-down; the chart below lists the thread, hex size, dimensions and price for each.

Bulk Discounts
50-99 any size: 5% off applied at checkout.
100-up any size: 10% off applied at checkout.

Size Chart

The hex is deliberately deformed to create the self-locking action, so an unused nut may measure slightly smaller across one set of flats than the others before it is installed. This is normal and is what makes it lock.

Reusing self-locking nuts

The locking feature wears with use. The general rule is that you should not be able to run the nut down its mating thread by hand once the locking portion engages. If you can turn the nut with your fingers past that point, it has done its service and should be replaced. When in doubt, fit a new one — at this price it is not worth the risk.

Notes

• SAE UNF (fine) threads only. These do not fit UNC (coarse) or metric fasteners.
• Plated steel. Some lots carry a moly lubricant coating over the plating; plating color may vary between lots.
• Sold individually. Order the quantity you need.