M4 x 6mm Flat Head T20 Stainless Bolt (qty x10)

Blue Alpine part F00113-00 is an M4 countersunk screw, 6 mm long, in stainless steel with a T20 drive. There are ten in the pack, and the pack costs $2.50.

Cutting the hole for an M4 countersunk screw

The screw is only half of a flush finish. The hole needs a cone cut into it at the same angle as the head, and deep enough that the top of the head ends level with the surface. Metric heads like this one are 90 degrees. Inch flat heads are 82, and countersink bits are sold in both angles, so read the marking on yours before you start.

Get the depth wrong and you’ll see it straight away. Too shallow and the head stands proud and snags things. Too deep and it sits below the surface in a dished hole, and on thin material that leaves very little edge around the hole to clamp. Mixed angles cause a quieter problem: a 90-degree head in an 82-degree recess touches at its outer edge only, so a narrow band is doing all the clamping. Wikipedia’s countersink page has drawings of both styles.

Which M4 countersunk screw length: 6 mm or 12 mm?

We sell this head in two lengths. Both are M4, both flat head, both T20. The M4 x 12 mm flat head is twice as long, and since countersunk screws are measured head and all, the extra 6 mm is all shank. The short one suits a thin part going into a thread that sits right behind it, like a press-in nut in sheet metal. If what you’re fastening is more than a couple of millimeters thick, a 6 mm M4 countersunk screw may not reach far enough to catch.

To check an old M4 countersunk screw, hold it against a ruler with the top of the head on zero. If the tip lands on 6, this is your part.

M4 or #8-32?

The inch size closest to M4 is #8-32: about 4.17 mm across, with 32 threads per inch, or roughly 0.79 mm pitch. This M4 countersunk screw is 4 mm with a 0.7 mm pitch. Either one will usually start in the other’s thread, then lock up within a turn or so. Not sure what the old screw was? Try it by hand in a known M4 nut. If it spins freely for several turns, it’s M4.

Driving an M4 countersunk screw

T20 is the bit. It’s the same size as on the M4 x 12 mm and several other screws we sell, so one T20 screwdriver covers a good part of the catalogue. Seat the bit fully, push in as you turn, and stop once the head is flush. A tapered head tightens fast as the cone wedges into its recess. Overdrive it and a short thread can strip in one go.

Torx recesses resist cam-out far better than Phillips. A bit with rounded lobes will still slip, though. If the tip looks shiny and soft-edged, replace it before it ruins a screw.

Stainless into aluminum

Stainless resists rust, which is why it’s used for small hardware that lives around moisture. There’s one catch worth knowing. When a stainless M4 countersunk screw goes into aluminum and the joint stays wet, the two metals can set up galvanic corrosion, and the aluminum around the screw slowly turns white and powdery. In a joint that’s dry most of the time it’s minor. Where it bothers you, a thin film of anti-seize on the threads is a common fix.

Spec

Ten screws. M4 x 0.7 metric coarse thread, 6 mm overall length, 90-degree flat head, T20 drive, stainless steel, Blue Alpine part F00113-00. If it’s going into sheet metal, our M4-3 self clinching nut has the same thread. A part number from your manual is the quickest way for us to confirm a match. Message us from the support page or call +1 (443) 514-5708.