#8 x 3/4" 410 Stainless Steel Truss Head Self-Tapping Sheet Metal Screw
Product Introduction
This isn't some generic hardware-store screw. It's a #8 x 3/4" truss head self-tapper made from 410 stainless — the workhorse grade for fasteners that need to cut threads into metal without mushrooming.
Here's the thing about 410SS most suppliers won't tell you: It's NOT as corrosion-proof as 304. Never will be. But here's what it IS — hardenable. We take it to HRC 38-45 through heat treatment, which gives you a screw that actually bites into cold-rolled steel and galvanized studs without stripping the threads or rounding the head. Try that with a 304 screw and watch what happens.
The truss head design matters more than you'd think. Wider bearing surface than a pan head. Lower profile than a hex washer head. It sits almost flush but distributes clamp load across roughly 40% more surface area. If you've ever had a pan head pull through thin sheet metal, you already know why this geometry exists.
We spec the point as Type A — sharp, not blunted. It'll start its own hole in anything from 18 gauge to 26 gauge sheet metal without a pilot. Thicker than that? Drill first. Don't skip that step and then blame the screw.
Typical production run tolerances: head diameter 0.350-0.362", thread major dia 0.161-0.167", length ±0.015". We check every batch against ASME B18.6.3. You get the certs.
Size Chart
Dimensional reference for #8 truss head self-tapping screws across available lengths:
|
Size |
Length (in) |
Length (mm) |
Major Dia |
TPI |
|
#8 x 1/2" |
1/2" |
12.7 |
0.164" |
18 |
|
#8 x 5/8" |
5/8" |
15.9 |
0.164" |
18 |
|
#8 x 3/4" |
3/4" |
19.1 |
0.164" |
18 |
|
#8 x 1" |
1" |
25.4 |
0.164" |
18 |
|
#8 x 1-1/4" |
1-1/4" |
31.8 |
0.164" |
18 |
|
#8 x 1-1/2" |
1-1/2" |
38.1 |
0.164" |
18 |
Head diameter: 0.350-0.362" across all lengths. Head height: 0.059-0.069". All truss head geometry consistent per ASME B18.6.3.
Pain Points & Solutions
|
Pain Point |
How Fasto Solves It |
|
Screw heads strip out before full engagement in cold-rolled steel |
We heat-treat 410SS to HRC 38-45. That's hard enough to drive the thread into CRS without the Phillips recess camming out. Our #2 recess geometry is ISO 7049 compliant — not some worn-out tooling. |
|
Truss head pulls through thin sheet metal under vibration |
Our head diameter is 0.350-0.362". That's a 40% larger bearing area than a standard pan head. For really thin material (24-26 ga), we recommend adding a backing washer — but honestly, most installs don't need it. |
|
Rust spotting after 6 months in semi-outdoor conditions |
410SS will tea-stain in wet environments. That's the tradeoff for hardness. But our passivation process (ASTM A967 nitric acid) maximizes the chromium oxide layer. For fully outdoor exposure, we'll tell you straight — use 304 or 316. For sheltered outdoor or indoor, this grade does the job. |
|
Inconsistent thread formation causes cross-threading in production |
We roll threads, don't cut them. Rolled threads are stronger by 20-30% and the surface finish is smoother. Our thread rolling dies get replaced on a fixed-cycle schedule, not when they fail. You get consistent thread geometry batch after batch. |
|
Screws won't start in harder sheet metal without walking or skating |
Type A sharp point with a 40-45° included angle. It bites and stays put. For material over 1.5mm thickness, drill a 3.3-3.5mm pilot hole. It's physics, not magic. |
|
Galvanic corrosion when used with aluminum panels |
410SS and aluminum are close enough on the galvanic series that it's generally not a problem in dry or indoor environments. For outdoor aluminum-to-steel joints in coastal areas, we'd steer you toward a coated fastener or 316SS instead. We'd rather lose the order than have you call back angry. |
Applications
Where these screws actually get used — not the marketing version, the real-world version.
HVAC & Ductwork
- Attaching duct flanges to galvanized sheet metal housings. The truss head won't sink through the thin metal the way a flat head does.
- Securing access panels where you need to remove and re-fasten repeatedly without stripping the hole.
- Mounting damper assemblies and control brackets to ductwork.
Metal Framing & Construction
- Steel stud-to-track connections in light-gauge commercial framing. 410SS gives you the hardness to drive through the track flange in one shot.
- Metal roofing panel attachment where a low-profile head matters for overlapping panels.
- Flashing and trim work on pre-engineered metal buildings. The passivated finish holds up against condensation cycles.
Automotive & Transportation
- Interior trim panel fastening. The wide truss head distributes pressure so you don't crack the plastic trim.
- License plate mounting. Magnetic 410SS simplifies installation if your line uses magnetic bit holders.
- Under-hood bracket attachment. Can handle moderate heat cycling and vibration without loosening.
Appliance & Equipment Assembly
- Sheet metal enclosure assembly for electrical cabinets, control boxes, and machinery guards.
- Appliance back panel fastening where a low-profile head prevents interference with adjacent components.
- General MRO (maintenance, repair, operations) across factories, warehouses, and field service trucks.
Why Work With Us?
We've been shipping fasteners out of China for over 20 years. Not dropshipping. Not trading. Actually manufacturing.
Our plant runs under IATF 16949 — that's the automotive quality management standard, not the generic ISO 9001 most fastener shops wave around. Every batch of 410SS wire we bring in gets spectro-tested before it hits the cold header. Composition check first, forming second. That way you're not discovering a chromium shortage halfway through a 50,000-piece run.
- IATF 16949 certified manufacturing facility
- Full material traceability — heat number to batch number to your PO
- In-house heat treatment with Rockwell verification on every lot
- CE, SGS, RoHS compliance documentation available on request
- ISO 898-1 / ASME B18.6.3 dimensional inspection before packing
- 20+ years exporting to North America, Europe, and Asia-Pacific markets
Full Specification Table
|
Parameter |
Specification |
|
Nominal Size (ASME) |
#8 |
|
Major Diameter |
0.164" (4.17 mm) |
|
Minor Diameter |
0.122" (3.10 mm) — Approx. |
|
Length (Nominal) |
3/4" (19.05 mm) |
|
Head Style |
Truss (Extra-Wide Low Profile) |
|
Head Diameter |
0.350"–0.362" (8.89–9.19 mm) |
|
Head Height |
0.059"–0.069" (1.50–1.75 mm) |
|
Drive Recess |
Phillips #2 (Cross Recess Type H) |
|
Thread Form |
Type A — Spaced Thread, Sharp Point |
|
Threads Per Inch (TPI) |
18 |
|
Pitch |
0.0556" (1.41 mm) |
|
Material Grade |
410 Martensitic Stainless Steel (UNS S41000 / EN 1.4006) |
|
Chemical Composition |
C 0.15% max, Cr 11.5-13.5%, Mn 1.0% max, Si 1.0% max, P 0.04% max, S 0.03% max |
|
Heat Treatment |
Quenched & Tempered to HRC 38–45 |
|
Tensile Strength |
Approx. 1,250–1,450 MPa (after heat treatment) |
|
Corrosion Resistance |
Moderate — suitable for indoor, sheltered outdoor, and mild chemical exposure |
|
Magnetic Properties |
Magnetic (ferritic-martensitic structure) |
|
Finish |
Passivated per ASTM A967 / Natural Stainless |
|
Applicable Standards |
DIN 7981 (Cross Recessed Tapping Screws), ASME B18.6.3, ISO 7049 |
|
Recommended Pilot Hole |
3.3–3.5 mm (for material > 1.5 mm thickness) |
|
Typical Sheet Metal Range |
18–26 Gauge (1.2–0.45 mm) — No Pilot Required |
|
Salt Spray Resistance |
48–96 hours (ASTM B117, passivated) |
|
Package Options |
Bulk carton, small box, blister card, poly bag with label |
These aren't hypothetical. Every one of these came from a customer who was losing money before they called us.
Real Problems We've Fixed
Problem #1: Screws keep stripping on the assembly line.
What's actually going on: The Phillips recess was poorly formed. Or the heat treatment left the head too soft. Sometimes both. Driver bit spins, head rounds out, line stops.
How we fixed it: We machine our punch tooling on CNC, not by hand. The recess geometry is dead consistent. Heat treat targets HRC 28–38 — hard enough the driver doesn't chew through it, soft enough the head doesn't snap off at torque. And if your line uses pneumatic drivers, switch to Pozi drive. PZ2 resists cam-out about 40% better than Phillips at the speeds you're running. We stock both.
Problem #2: Rust spots. Three months in, the customer wants a refund.
What's actually going on: Cheap zinc. Under 5 microns, probably not passivated properly. Or carbon steel spec'd for a bathroom cabinet — that's not a material problem, that's a spec problem.
How we fixed it: We stock three corrosion tiers so you pick the right one. Standard zinc: 8–12 microns, good for indoor furniture in dry climates. Yellow zinc: 12–15 microns with a thicker chromate layer, handles kitchen humidity fine. Stainless A2-304: 200+ hours salt spray, for bathrooms, coastal homes, outdoor-adjacent. The price jumps about 2–3× between zinc and stainless. Most of our customers use stainless just on the moisture-exposed assemblies — under sink, near dishwasher — and zinc everywhere else.
Problem #3: Thread strips out of the particleboard. Joint works loose.
What's actually going on: Standard wood screws in engineered wood. The thread pitch is too fine — it's cutting individual channels instead of grabbing a big chunk of material. Plus the pilot hole was probably drilled at full diameter instead of 85% of the minor thread diameter.
How we fixed it: Confirmat screws. That's the fix. Deep, widely-spaced thread that displaces material outward instead of cutting through it. You get about 60% more pull-out resistance in particleboard compared to a same-length wood screw. We'll send you the pilot hole chart for every diameter we stock. Use it. A correctly sized pilot hole is the difference between holding 80 kg and pulling out at 30 kg.
Problem #4: Hardware bags are wrong. Missing screws, wrong quantities, angry customers.
What's actually going on: Manual counting. Someone on the packing line is counting screws by hand for eight hours a day. Mistakes happen. Usually around 3 PM.
How we fixed it: We pre-sort and kit everything. Each bag goes through a weight check first, then an optical counter for verification. If the count is off by even one screw, the line stops and the bag gets reworked. Your logo on the bag, barcode with the SKU, bilingual instructions inside if you want them. The kit drops straight into your flat-pack carton — no repacking, no recounting, no customer service emails about missing hardware.
Problem #5: Screw heads sit proud of the panel surface.
What's actually going on: Countersink angle doesn't match the screw head. Or there's a burr under the head from worn tooling. Or the head diameter varies too much from piece to piece.
How we fixed it: All our countersunk screws use a 90° underside angle, burr-free. Head diameter tolerance is ±0.2 mm. That's tight enough that if your panel shop is using a matching 90° countersink bit, the heads seat flush. Every time. We'll include the recommended countersink bit spec with your first order so your production team has the exact match.
FAQ:
Q1: Can 410 stainless steel screws rust? Are they OK for outdoor use?
Short answer: yes, they can. Longer answer: 410SS contains 11.5-13.5% chromium. That's enough to form a passive oxide layer that prevents red rust in most indoor and sheltered outdoor conditions. But it's NOT 304. Put it in direct rain and sun for a year and you'll see surface tea-staining — a light brown discoloration that's cosmetic, not structural. For fully exposed outdoor applications, especially within 5 miles of a coastline, step up to 304 or 316. For everything else — HVAC ducts under roof, interior metal studs, automotive interior trim — 410 is the right call. You're trading a bit of corrosion resistance for a lot more hardness.
Q2: Do I need to pre-drill a pilot hole?
Depends on the material thickness. For 18-26 gauge sheet metal (roughly 0.45-1.2mm), no pilot hole needed. The Type A sharp point starts its own hole and the thread follows. For anything thicker than 1.5mm (about 16 gauge and up), drill a 3.3-3.5mm pilot hole first. Skip this step and you'll either snap the screw or burn the tip. You'll feel the difference on the drill immediately — if it's fighting you before the first thread engages, back out and drill.
Q3: What's the difference between self-tapping and self-drilling?
Self-tapping screws (like this one) have a sharp point that pierces the material, then cut or form their own threads as they're driven in. They need the material to be thin enough for the point to penetrate. Self-drilling screws have an actual drill-bit tip — fluted cutting edges that bore through metal like a twist drill. They can handle thicker material, but they're more expensive and the drill tip snaps if you hit anything hard. For sheet metal under 1.5mm, self-tapping is faster and cheaper. For structural steel 2mm+, use a self-driller. Two different tools for two different jobs.
Q4: Can these screws go through stainless steel sheet?
No. Not directly. 410SS self-tappers work great going into carbon steel, galvanized steel, aluminum, and most non-ferrous sheet metals. But stainless-on-stainless is a different game. The material is too hard and too gummy. You'd need a self-drilling screw with a carbide tip or a pre-drilled hole + tap. We get this question a lot from guys building food-grade equipment. If that's your application, contact us and we'll spec the right fastener instead of watching you waste a box of these.
Q5: Why choose a truss head over a pan head?
It's about clamp distribution. A pan head concentrates clamp force on a smaller ring of material. A truss head spreads that same torque across roughly 40% more surface area. For thin sheet metal, that's the difference between a solid joint and a screw that pulls through after 500 vibration cycles. The tradeoff: truss heads sit slightly proud of the surface compared to flat heads. If you need a truly flush installation, you'd countersink with a flat head. If you need holding power with minimal intrusion, truss wins.
Q6: How do cam locks actually work?
The bolt screws into one panel first. The cam — that disc-shaped nut — sits in a drilled hole in the edge of the mating panel. When you turn the cam with a screwdriver, the channel inside it is eccentric, so it pulls the bolt head toward the center of the cam as it rotates. That draws the two panels tight. No glue. You can take it apart and reassemble it. That's the whole point of flat-pack. Our kits are tested for 500+ cycles without loosening. After about cycle 300, you might feel a tiny bit of play. By cycle 500, it's still holding — just not quite as snug as the first assembly.
Q7:Will these work with aluminum without causing galvanic corrosion?
Generally yes, with a caveat. 410 stainless and aluminum are about 0.3-0.4V apart on the galvanic series in most environments. That's below the 0.5V threshold where galvanic corrosion becomes a real concern. In dry or indoor applications, you won't have issues. In wet outdoor conditions — especially if the joint sees salt spray or de-icing chemicals — the aluminum will sacrifice itself to protect the stainless screw. The screw will look fine, but the aluminum around the hole will slowly pit. For outdoor aluminum joints, we recommend using a nylon washer or coating the screw to break the electrical path. Or go with aluminum rivets if the application allows.
Q8: What's the recommended installation torque?
For #8 self-tapping screws into 18-22 ga steel, target 18-22 in-lbs seating torque. Use a clutch-driver set to about 60% of max and dial up from there. The rule on the floor: stop when the head contacts the surface plus a quarter-turn. Over-torquing strips the freshly cut threads — and now you've got a loose screw and a ruined hole. If you're running these on an assembly line with torque-controlled drivers, 15-18 in-lbs gives you a consistent clamp without thread damage.