The pilot hole is the slowest step in metal roofing — or it was, until self-drilling fasteners put a miniature drill bit on the tip of the screw. Teks self drilling roofing screws, made under the Teks brand now owned by ITW Buildex, drill their own hole, tap their own threads, and clamp a sealing washer in one motion, which is why “Teks” has become shorthand on jobsites for the entire self-driller category. Used correctly, they make a metal roof or steel-framed structure faster to build and genuinely watertight. Used with the wrong point, wrong length, or an over-aggressive impact driver, they strip, leak, and back out. This guide covers how the fastener actually works and the specs that matter when you are standing in the fastener aisle.
How a Self-Driller Differs From a Self-Tapper
The terms get swapped constantly, and the difference matters. A self-tapping screw cuts threads into an existing hole — you still drill a pilot. A self-drilling screw carries a fluted drill point (the milled tip that looks like a tiny twist bit) that bores through steel before the threads ever engage. Every Teks is self-drilling; not every “metal screw” is. On roofing, the practical payoff is one-tool, one-pass fastening: a 1,500 sq ft metal roof takes roughly 1,200 to 1,800 screws, and eliminating a pilot-drill step on each one saves hours.
Drill Point Numbers: The Spec Most People Ignore
The number stamped after the point — #1 through #5 — describes the drill tip’s length and capacity, and it must match the steel you are drilling:
- #1 and #2 points: Thin material, roughly 0.035 inch up to about 0.090 inch total steel. This covers standard 29 and 26 gauge roof panels into light-gauge purlins.
- #3 point: The general-purpose choice, drilling up to about 0.14 inch — panel plus 14 to 12 gauge steel framing.
- #4 and #4.5 points: Up to roughly 0.25 inch of steel; structural connections and heavy purlins.
- #5 point: Thick structural steel to 1/2 inch. Overkill for roofing panels, standard for red-iron framing.
The point must fully penetrate the steel before threads engage — that is why heavier points have longer unthreaded pilot sections. Run a #5 into thin sheet and the long point leaves threads barely engaged; run a #1 into quarter-inch plate and the tip burns up before it is through. Match the number to the stack thickness and the screw does the rest.
Metal-to-Wood vs. Metal-to-Metal Roofing Screws
Roofing screws split into two families, and mixing them up is the most common DIY error. Metal-to-wood screws — the majority of residential metal-over-purlin and metal-over-deck jobs — carry a Type 17 or small drill point that pierces the panel, then coarse wood threads that bite framing lumber or plywood. Common sizes are #9 and #10 diameter in 1, 1.5, 2, and 3 inch lengths; a 1.5 inch screw handles panel-to-purlin, while 3 inch reaches through ridge closures and trim stacks. Metal-to-metal Teks (#12 or #14 diameter, fine machine threads, #3 to #5 points) are for steel purlins, carports, and pole barns with steel secondary framing. Both types for exposed roofing carry a bonded EPDM sealing washer under a steel cap — the washer is the waterproofing, and everything about good installation technique revolves around treating it properly.
Coatings, Colors, and Corrosion
A roof screw fails by corrosion long before it fails mechanically, so coating class matters. Basic zinc-plated screws are attic-and-interior grade only. For exposed roofing, look for proprietary multi-layer coatings — Teks’ climate-rated lines and equivalents from SFS, Atlas, and ST Fastening carry 1,000-plus hour salt spray ratings — or stainless-capped heads. Painted heads color-matched to panel systems (charcoal, galvalume, rustic red, forest green, and a couple dozen others) cost a cent or two more per screw and disappear visually on the finished roof. One metallurgy rule is absolute: never use plain carbon-steel fasteners on aluminum panels or copper flashing; galvanic reaction will eat the panel around the screw. Use stainless or specifically compatible coated fasteners on dissimilar metals.
Driving Technique: Where Leaks Are Made
Self-drillers want speed and steady pressure, not hammering. Use a drill or a screw gun with an adjustable clutch — set 2,500 RPM or less for wood substrates and around 1,000 to 2,000 RPM for steel — and skip the impact driver: impacts shatter drill points, spin out washers, and make torque control impossible. Then obey the washer:
- Drive perpendicular. A screw angled more than a few degrees loads one edge of the EPDM washer and leaves the other edge open. Crooked screws are the number-one leak source on DIY metal roofs.
- Stop at snug. Correct compression squeezes the EPDM just to the washer’s steel rim — you should see a slight rubber bulge, not rubber squirting past the cap. Overdriving dishes the panel and splits the washer; underdriving leaves it loose enough to pump water in wind-driven rain.
- Fasten in the flat, per the panel maker. Most exposed-fastener panels (classic rib, R-panel, ag panel) spec screws in the flat next to the rib, where the washer seats on solid support. Some manufacturers spec rib fastening; follow the panel sheet, not habit.
- Hit the framing. Screws into decking gaps or missed purlins hold nothing. Chalk-line every purlin row before you start a run.
Head Styles and Driver Bits
Exposed roofing Teks overwhelmingly use a 1/4 or 5/16 inch hex washer head, driven with a magnetic hex socket — buy the quality impact-rated sockets in three-packs, because a worn socket wobbles and lets the screw tilt at the critical seating moment. Pancake-head and wafer-head self-drillers exist for concealed-fastener panel clips and interior framing, where a low-profile head must sit flush under the next panel; do not substitute hex heads there, as the bump telegraphs through standing-seam panels. A #2 or #3 Phillips version shows up on light-gauge steel framing screws, but for roofing, hex is the standard for a reason: the socket grips positively at the higher torque these screws need, with no cam-out chewing the painted head. Keep a dedicated depth-sensing nosepiece or a screw gun with an adjustable depth collar for production runs — it seats every washer identically, which is exactly the consistency hand-feathering a drill trigger cannot match across 1,500 fasteners.
Buying and Budgeting
Expect to pay $30 to $60 per 250-count bag for #10 x 1.5 inch painted metal-to-wood roofing Teks, and $40 to $80 for #12 metal-to-metal in comparable counts — roughly $0.12 to $0.30 per screw. Figure about 80 screws per roofing square (100 sq ft) at typical 24-inch purlin spacing with fasteners every rib flat, then add 10 percent. For a 20 x 30 shop roof, that is around 500 to 600 screws, a $75 to $150 line item. Buy all one brand and batch: mixed-source screws vary a sixteenth in head size, which shows when a socket suddenly slips, and painted color lots vary just enough to see.
Maintenance and Replacement
Storage habits affect performance more than most buyers realize. Keep opened bags sealed and dry — surface rust starting on a shelf in the garage continues on the roof, and a rusty drill point drills noticeably slower and hotter. Cold screws also drill slower in cold steel; on winter jobs, keeping the day’s fasteners in a heated cab measurably improves point life. And when a point does burn up mid-panel (it happens on thick purlins), back the screw out and start a fresh one an inch away rather than forcing it — a spun, half-drilled hole with a snapped point in it is a future leak wearing a screw head.
EPDM washers are the roof’s consumable. UV and thermal cycling harden them over 10 to 20 years, and panels expanding against fixed screws can slowly loosen fasteners — the origin of the “walk the roof every few years” advice for exposed-fastener systems. Check for backed-out heads, spun washers, and rust halos. Replace a failed fastener with the next diameter up (a #12 replaces a stripped #9/#10 hole, a #14 replaces a #12) so fresh threads bite solid material, never by reusing the wallowed hole. Ten minutes with a driver and a bag of oversized replacement screws every few springs is the entire maintenance program — a fair trade for the fastest fastening system in roofing.
