M4 x 50mm Pan Head Philips Stainless Bolt (qty x10)

An M4 x 50mm screw is long for its diameter: 50 mm of shank under a pan head, only 4 mm across the thread. These are stainless steel with a Phillips drive, ten per pack, at $6.62. Blue Alpine’s part number is F00120-00.

Measuring a long M4 x 50mm screw

On a pan head, length runs from the underside of the head to the tip. Put a ruler or calipers along the shank and you should read 50 mm. That’s 1.97 in, which is where the confusion starts. It’s easy to take one for a 2 in imperial screw, and the common one in that size is #8-32.

The two don’t mix. A #8-32 is about 4.2 mm across with 32 threads per inch, close to 0.79 mm per turn. M4 is 4 mm with a 0.7 mm pitch. Over a long thread that difference adds up fast, and a nut or tapped hole made for one will bind on the other within a few turns. The Unified Thread Standard page lists the imperial sizes if you want to compare.

A quick check: 10 mm of an M4 thread holds about fourteen crests. Lay a ruler alongside and count.

Threaded all the way?

Long screws are sometimes threaded only partway, with a plain shank under the head. The listing doesn’t say whether this M4 x 50mm screw is fully threaded. If you need thread right up to the head, look closely at the photo or ask us before ordering.

Working out a stack for an M4 x 50mm screw

A screw this long is usually passing through something before it reaches its thread: a spacer, a stack of parts, or a thick block. Add every layer from under the head down, then add the thread engagement you want at the far end. For M4 in steel, aim for at least 4 mm of engagement, more in softer metal.

Here’s an example with parts we carry. Our M4 nylon spacer is 19 mm long, which leaves 31 mm of an M4 x 50mm screw for everything else. Nylon is softer than metal, so snug the screw rather than cranking it, or the spacer can crush.

Clinch nuts at the far end

If the screw finishes in a self-clinching nut, match the nut to the panel as well as the thread. The dash number on these nuts, M4-2 or M4-3, is the shank code tied to minimum sheet thickness and hole size. Both are M4 inside, so an M4 x 50mm screw threads into either one.

Driving an M4 x 50mm screw straight

A pan head M4 takes a PH2 bit. A PH1 is too small and slips; a PH3 won’t seat. With a long screw, the bigger issue is alignment. Any tilt at the head turns into a sideways push at the tip, and the screw starts its thread crooked.

• Start it by hand for the first several turns, eyeballing from two directions.
• Keep the driver in line with the screw the whole way down.
• Use a power driver on low speed only, and stop short to finish by hand.
• On stainless into a stainless thread, a little anti-seize helps keep the long thread travel from galling partway.

Back off and restart if it gets tight early. Forcing a crooked M4 x 50mm screw can strip the first threads of the hole.

Cutting an M4 x 50mm screw shorter

If 50 mm is more than you need, you can cut it down. Thread a plain M4 nut past the cut line first. Clamp the screw in a vise with soft jaws, or hold it by the piece you’re cutting off, so the thread you keep isn’t crushed. Cut with a hacksaw and file a small chamfer on the end. Then unscrew the nut. It cleans up the cut thread on the way off. We don’t list a plain M4 nut, but any hardware store has one.

Questions before you order

This is the longest M4 screw in our fasteners and tools range. If your parts list calls for something else, or you’d like the length confirmed against your old one, call +1 (443) 514-5708.