Sheet Metal Screws and Self-Drilling Screws

A sheet metal screw is threaded all the way to the head and cuts or forms its own threads as it goes in, so it holds in thin metal without a nut on the back. The first choice is whether the screw has to make its own hole. That decides which of WBC’s three kinds you want.

Reading the size

A sheet metal screw size like #8 x 1 is two numbers. The #8 is the diameter: the bigger the number, the thicker the screw. Sizes #6 through #14 cover most jobs. The 1 is the length in inches, measured from under the head to the tip for hex and pan heads.

Thicker screws hold more and need a bigger hole; length should be enough to go through what you’re fastening and fully engage the metal behind it, without poking out where it’ll catch a hand or a wire.

Self-drilling hex washer head screws: no pilot hole

These have a small drill bit for a tip. Drive one with a drill and it drills, taps and fastens in one pass, so you don’t need to drill a pilot hole first. That’s what you want for fastening sheet metal to metal framing, a steel stud, a shop wall girt or a trailer panel, where you’d otherwise be drilling every hole twice.

The hex washer head takes a nut driver in the drill, which holds the screw straight and doesn’t cam out like a Phillips can. The washer built under the head spreads the load on thin metal.

Diameter	WBC lengths
#8	1/2, 1, 1-1/2 in.
#10	3/4, 1, 1-1/4 in.
#12	3/4, 1-1/2, 2, 2-1/2 in.
#14	3/4, 1, 1-1/2, 2, 2-1/2, 3 in.

The drill point has limits: it’s made to get through a certain thickness of steel. The drill point has to cut all the way through the metal before the threads reach it, so a point too short or too light for thick steel won’t get there no matter how long the screw is. Check the package for the steel thickness the point is rated to drill.

Slotted hex washer head sheet metal screws: pointed, for pre-drilled or thin metal

These have a sharp point rather than a drill tip. Depending on the screw and the sheet, they can start in very thin sheet metal on their own; in most metal they go into a pre-drilled hole. The hex washer head drives with a nut driver, and the slot gives you a screwdriver option in a tight spot.

Diameter	WBC lengths
#6	3/8, 5/8 in.
#8	3/8, 1-1/4, 1-3/4, 2, 2-1/2 in.
#10	3/8, 1/2 in.
#12	1, 1-1/2, 3 in.

The short #6, #8 and #10 lengths, 3/8 and 1/2 inch, are the ductwork and panel screws: joining duct sections, closing up a furnace or appliance panel, a vent cap. Short means nothing sticks far into the duct to catch dust.

Combo-drive pan head sheet metal screws: the general-purpose screw

A pan head has a rounded top that sits above the surface. “Combo” drive takes either a Phillips or a slotted screwdriver. These are the everyday sheet metal screws for electrical boxes, panels, brackets, and fastening thin metal or plastic to wood.

Diameter	WBC lengths
#4	1/2, 1 in.
#8	1/2, 1 in.
#10	1/2, 1-1/2, 2 in.
#12	1/2, 1-1/4 in.
#14	1, 1-1/2, 2 in.

Can you use sheet metal screws in wood?

Yes, they’re often used to fasten metal or plastic to wood, and their full-length threads bite well. For wood-to-wood framing or anything carrying load, use fasteners made and rated for that job.

Out in the weather

Plain steel screws rust outside. On a Montana shop or barn, where snowmelt and spring runoff keep the lower walls wet, use a coated or corrosion-resistant screw for exterior metal, and match it to the metal it’s going into.

The Pick

For metal to metal framing without pilot holes, self-drilling hex washer head screws: #10 or #12 for most sheet-to-framing work, #14 for heavier connections. For ductwork and appliance panels, the short slotted hex washer head screws. For general fastening of thin metal and plastic, the combo pan heads.

Frequently Asked Questions

What does #8 x 1 mean on a screw?

#8 is the diameter size, and 1 is the length in inches. Higher numbers are thicker screws.

Do I need to drill a pilot hole for sheet metal screws?

Not for self-drilling screws, which drill their own hole within their rated thickness. Pointed screws can sometimes start in very thin sheet; in most metal they need a pilot hole.

What’s the difference between self-drilling and self-tapping screws?

Self-tapping screws cut or form their own threads. Self-drilling screws are a kind of self-tapping screw with a drill tip, so they also make their own hole.

What size sheet metal screw for ductwork?

Short screws, usually #8 or #10 at 3/8 or 1/2 inch, so they hold the joint without sticking far into the duct.