M5 x 15 Washer Stainless (qty x10)

Each M5 washer in this pack is stainless steel with a 15 mm outside diameter, which makes it a wide one for the size. Ten per pack at $2.50. Blue Alpine part number F00123-00, listed as “M5 x 15”.

15 mm is the wide M5 washer

The “M5” tells you the screw size it’s made for. The “15” is the outside diameter in millimeters. A standard M5 flat washer is only about 10 mm across. The 15 mm size is the one listed for M5 in the large-washer standards, DIN 9021 and ISO 7093.

That extra 5 mm makes more difference than it sounds. With the usual 5.3 mm hole in the middle, a 15 mm washer has close to three times the bearing area of a 10 mm one. The clamping load from the nut or screw head spreads over a much bigger patch of material.

Thickness isn’t part of the listing. If it matters to your stack, measure your old washer and ask us.

Jobs a wide M5 washer suits

• Thin sheet that would dish or dent under a small washer.
• Plastic and other soft materials that creep or crack under a concentrated load.
• Oversized, slotted or worn holes, where a standard washer could pull partly into the hole.
• Bridging a hole that’s been drilled slightly off, so the head still has something solid to bear on.

And jobs it doesn’t

Never put any M5 washer under a countersunk head. The head is meant to sit in its cone; a washer holds it up and ruins the fit. All three M5 screws we sell are flat head, so with those the washer belongs under the nut, if there is one.

It also won’t stop anything loosening. A flat washer spreads load and protects the surface, nothing more. If vibration is backing a nut off, use a drop of low-strength threadlocker or a second nut. And check the space around the hole: a 15 mm washer needs 7.5 mm clear from the screw center in every direction, which rules it out right next to a wall or a bend.

Why a stainless M5 washer

Washers sit right at the joint, where water collects and dries out again. A plain steel washer in that spot rusts from its edges first, and the rust can bleed onto the panel around it and make the joint harder to undo later. A stainless M5 washer avoids both problems. At $2.50 for ten, stainless is the easy call for a damp spot.

Measuring an old washer

Calipers give you three numbers: hole, outside diameter and thickness. For an M5 washer, the hole is normally a little over 5 mm so the screw passes freely. If your old one measures around 10 mm outside, it’s the standard size and these will be noticeably bigger. Check that the larger one clears nearby edges before you swap.

A hole well under 5 mm points to an M4 washer. One around 6.4 mm is the usual M6 size. Neither is this part.

Order of parts on a through-bolt

Head, then your parts, then a washer, then the nut. Put the M5 washer under whichever piece you’ll turn while tightening. Usually that’s the nut. The washer stops the turning nut from scoring the surface and gives it a smooth face to slide on, so the torque you apply goes into clamping instead of friction.

If the head side bears on soft material too, add a second washer there, as long as it’s a pan or hex head and not a countersunk one.

Matching M5 hardware

The M5 screws and the M5 hex nut we list are stainless too, so a full set won’t mix metals. Besides the 20 mm screw above, there’s an M5 x 12mm flat head for thinner stacks. Wikipedia’s washer page covers the other types if you’re comparing. Questions about a specific part number? Email us through the support page.