M5 x 0.8 Hex Nut Stainless (qty x10)

This M5 nut is a plain six-sided hex nut in stainless steel, threaded M5 x 0.8. The pack has ten. It’s Blue Alpine part F00122-00 and costs $2.50.

What “M5 x 0.8” tells you

M5 is the thread size: 5 mm nominal diameter. The 0.8 is the pitch, the distance from one thread crest to the next, and 0.8 mm is the standard coarse pitch for M5. Nearly every M5 screw you’ll come across is coarse. A fine-pitch M5 x 0.5 exists, but it’s uncommon, and it won’t go into this nut.

Any of our stainless M5 screws will thread into this M5 nut, from the 8 mm countersunk up to the 20 mm flat head.

The #10-32 lookalike

This is the classic mix-up with metric nuts. A #10-32 screw is about 4.8 mm across, with 32 threads per inch. That works out to roughly 0.79 mm per thread. On paper it’s nearly identical to M5 x 0.8, and in your hand it looks the same.

It isn’t. A #10-32 will usually start in an M5 nut and spin a few turns, then either bind or sit loose on the slightly smaller diameter and strip under load. If a screw goes in easily for three turns and then stops dead, don’t force it. Check whether it’s imperial.

The quick test is simple: an M5 nut should spin by hand along the whole thread of a matching screw with no tight spots.

Wrench size for an M5 nut

A standard M5 hex nut takes an 8 mm wrench, socket or nut driver across the flats. Measure yours if you want to be sure; the calipers should read close to 8 mm between opposite flat sides.

Avoid adjustable wrenches on a nut this small. The jaws flex, the corners round over, and then nothing grips it properly. A nut driver is the best tool. It covers all six flats and lets you hold the nut steady in a tight space while the screw is turned from the other side.

Stainless on stainless: watch for galling

Run a stainless M5 nut onto a stainless screw too fast, or with grit in the threads, and the two surfaces can tear and cold-weld together partway down. That’s galling. It feels like the nut suddenly got tight for no reason.

• Clean both threads. A bit of debris is enough to start it.
• Turn it by hand until it’s close, then finish with the driver.
• Go slowly. Heat from a power tool makes it worse.
• A light smear of anti-seize on the screw thread helps a lot.

If a nut does lock up halfway, stop. Forcing it further usually twists the screw off. Occasionally backing it off a quarter turn with a drop of oil frees it. More often it has to be cut off and replaced along with the screw.

A plain M5 nut doesn’t lock

Nothing on this nut resists loosening. In a joint that vibrates, a plain M5 nut can back off over time. You have two easy fixes. Add a drop of low-strength threadlocker, or run a second nut down tight against the first as a jam nut. A washer under it protects the surface but won’t stop it turning.

Leave at least a full thread or two showing past the M5 nut once it’s tight. If the screw ends inside the nut, you’re only using part of its threads. The M5 x 20mm flat head screw gives the most length to work with.

When a loose nut isn’t practical

A hex nut needs a hand or a tool on the far side of the panel every time the screw comes out. A self-clinching nut is pressed into the sheet once, while you can still reach both sides, and after that the screw threads straight into the panel. Our M5-3 clinch nut is one option. The dash number relates to the sheet thickness, so match it to your panel. Wikipedia’s nut article covers the other styles. For anything else, call +1 (443) 514-5708 or browse fasteners and tools.