Self-Drilling Screws: Point Size, Material and Metal Thickness

Pick a self-drilling screw by the total thickness of metal it has to drill, then by material. On Fastenio's product pages, a #1 drill point handles steel up to about 0.050 in (18 gauge), a #2 point about 0.035 to 0.100 in (20 to 12 gauge), and a #3 point about 0.100 to 0.175 in (12 to 7 gauge). The point has to finish drilling all the way through before the threads reach the metal, so measure the whole stack, including any gap or insulation between layers.

For material, 410 stainless is the one to use when the screw has to drill steel: Fastenio's 410 product pages describe it as hardened so the point drills steel. The 18-8, 305 and 316 self-drillers are listed as best for aluminum and light-gauge steel, and they resist corrosion better. If you still need to decide between a self-drilling screw and a self-tapping screw with a pilot hole, start with our guide to which screw to use for sheet metal. This article picks up once you know you want a self-drilling one.

What do the drill point numbers mean?

The number on a self-drilling screw (#1, #2, #3) describes the drill point at the tip, not the screw diameter. A higher number means a longer point that can drill thicker metal. Hilti's Direct Fastening Technical Guide (section 3.6.1, "Self-Drilling Screw Fastener Selection and Design") explains what sets that capacity. The length of the drill flute decides how thick a piece of metal the screw can drill, because the flute is the channel the chips leave through. The unthreaded length from the tip to the first thread has to be long enough for drilling to finish before that thread engages.

These are the ranges printed on Fastenio's self-drilling screw product pages. The same point number lists the same range across the screw diameters checked, from #8 to #14.

Source: Fastenio product pages for #8 #1-point, #8 #2-point, #12 #2-point, and #10, #12 and #14 #3-point self-drilling screws (checked 2026-11-06). Other manufacturers publish their own charts, and they don't all agree, so for another brand use that maker's table.

The catalog's self-drilling screws stop at #3. For steel thicker than about 0.175 in, these screws are the wrong fastener. Drill and tap the hole, or use a bolt and nut.

Why does the total thickness matter more than the top sheet?

Because the threads move much faster than the drill. Hilti's guide states that screw threads advance up to ten times faster than the drill flute can remove metal, so all drilling has to be done before the threads start to form. If the point is still cutting when the first thread reaches the top sheet, the threads try to pull the screw forward faster than the point can cut, and the point jams. The same guide warns that a flute buried completely in the material traps its chips, cutting stops, and the point burns up or breaks.

So add up everything the point has to pass through:

• the top sheet (or the flange of a clip or angle)
• any gap, insulation or sealant between the layers
• the bottom sheet or the steel member

Hilti's drawing measures "total thickness to be drilled" across all three. Two 16-gauge sheets with a gap between them can need a longer point than either sheet alone suggests.

Which self-drilling screw material drills steel?

Fastenio lists self-drilling screws in five materials. The product pages describe them this way:

One thing to read carefully: the 18-8, 305 and 316 pages print the standard drilling range for their point number, but the same pages say these screws are best for aluminum and light-gauge steel. The 18-8 page also says to use 410 for heavier steel. Go by that advice. If an 18-8 or 316 screw has to drill steel near the top of its point's range, check the full product spec before you commit a job to it.

For how 410 compares with 18-8 and 316 on corrosion, see the 18-8 vs. other grades guide. Hilti's guide makes the same trade-off plain in a footnote. 410 has chromium but no nickel, which "reduces corrosion resistance significantly" compared with 18-8 and 316. Hilti also notes that most 400-series stainless steels, 410 included, are generally considered susceptible to hydrogen-assisted stress corrosion cracking.

What if the screw has to go through wood into metal?

Wood over steel is a separate case. Hilti's guide says that when you drill through wood more than 1/2 in thick into metal, you need a clearance hole. Its answer is a screw with breakaway reamer wings, which ream a clearance hole through the wood and snap off when they hit the metal. Fastenio's self-drilling screw catalog doesn't list winged screws. With a Fastenio screw, drill a clearance hole through the wood first so the threads don't grab the wood before the point is through the steel.

How fast should you drive a self-drilling screw?

Use a variable-speed screw gun, keep the screw square to the surface, and let the point cut. Hilti's installation instructions say to install self-drilling screws perpendicular to the work and not to apply excessive pressure. Too much pressure slows the screwdriver, and Hilti says that can lead to drill tip failure. For reference, the guide lists a Hilti screwdriver with a 2,500 rpm motor for self-drilling screws in steel up to 1/4 in thick and one with an 1,800 rpm motor for steel up to 1/2 in. Those are the speeds of Hilti's own tools, not a universal setting, so follow the screw maker's or tool maker's guidance for the screw in your hand.

Once the point is through and the threads pull the head down, ease off. A hex washer head with a depth-setting nosepiece or a clutch stops you overdriving it and stripping the threads in thin sheet. If a stainless screw stops turning partway in, don't force it. Our article on stainless steel galling explains what's happening.

Which head style should you choose?

The catalog carries self-drilling screws with hex washer, Phillips pan, flat (countersunk), truss, modified truss, wafer and square-drive pan heads. As a quick guide:

• Hex washer head: the built-in washer face spreads the load, and the external hex suits a nut driver for fast, straight driving. This is the common choice for HVAC, roofing and framing. One 316 version comes with a bonded sealing washer to seal the hole against water.
• Pan and truss heads: a low, wide bearing face for fastening thin sheet or trim where a hex would snag.
• Flat head: sits flush in a countersunk hole.

Head dimensions (head diameter, height and drive size) for each part are listed in the technical specs and on each product page.

The bottom line

Measure everything the point has to pass through, including gaps, and choose the drill point whose range covers it: #1 up to about 0.050 in, #2 about 0.035 to 0.100 in, #3 about 0.100 to 0.175 in, per the product pages. Use 410 stainless when the screw has to drill steel. Use 18-8, 305 or 316 for aluminum and light-gauge steel where corrosion resistance comes first. Drive at a steady, moderate speed without leaning on the gun.

Shop self-drilling screws by point, material and head. Where you already have a pilot hole, use sheet metal screws or thread cutting screws instead.