Hex Seal Screw (Sharp Point, Class 4)

What a needle point stitching screw with seal is for

Hobson calls this screw a metal stitching screw, flange hex head with seal: a self-drilling screw with a needle point, a hex head with a built-in flange and a seal under it, Class 4 coated to AS 3566. Hobson lists it for general fixing of lightweight steel, sheet metal stitching and thin gauge sheet steel. On a roof or wall, that means pulling the overlapping side laps of the sheets, or a flashing and a sheet, tight together.

Hobson's self-drilling screw identification sheet describes the needle point as the point used on screws of a general purpose nature, and the seal (also called a neo, washer or EPDM) as designed for a watertight seal. That seal is the difference from our plain flange hex stitching screws, which come in the same two sizes without one.

Stitching screws hold sheet to sheet. To fix sheeting down to steel purlins or battens, use roofing screws or tek screws with a point made for that steel.

Which size: #8-15 x 12mm or #10-12 x 20mm?

• •Size is gauge and threads per inch (TPI) x length. Hobson's gauge chart gives 8 gauge as 4.2mm and 10 gauge as 4.8mm across the thread. Both are coarse thread by Hobson's definition (up to 16 TPI): 15 TPI on the #8 and 12 TPI on the #10.
• •Length: Hobson measures hex screws with a flange and seal from under the head, so 12mm and 20mm are the lengths below the seal. Choose a length that passes through all the laps.
• •Drive: the #8-15 takes a 1/4 inch hex nut setter, the #10-12 a 5/16 inch one. Hobson recommends the 1/4 inch x 45 or 65mm magnetic nut setters for the #8, and the 5/16 inch x 45 or 65mm Impax magnetic nut setters for the #10.
• •Holding power: in Hobson's test in 0.55mm G550 sheet, the #10-12 x 20mm has close to twice the pull-out of the #8-15 x 12mm (see the table below).

Sizes and head dimensions

Both sizes we carry, from Hobson's performance data sheets. Select a row to open that screw.

Pull-out and strength values Hobson publishes

Hobson publishes laboratory values for both screws, measured in 0.55mm G550 steel sheet only. Hobson notes that actual pull-out loads may differ with the properties of the base material and that safety factors should be considered for design, so these figures do not carry over to other sheet thicknesses or grades. Hobson gives no edge distance or spacing values; the figures are for single screws in the lab. Hobson's drill test for both is a 13kg load at 2,200 RPM through 0.55mm G550, in no more than 1.5 seconds per screw and 1.0 second on average. Hobson does not publish a thickest sheet they will drill.

Class 4 coating, exposure and Hobson's warranty

Class 4 is a corrosion class for self-drilling screws (AS 3566). Hobson's finish comparison describes its Class 4 coating as mechanically galvanised, 38 microns, high corrosion resistance, for external use in a severe marine environment (ISO 9223 corrosivity category C4). That suits exposed roof and wall sheeting in C2, C3 and C4 environments, but not C5 (see below). Hobson's material for these screws is hardened C1022 steel.

Hobson's self-drilling screw warranty (effective September 2025, doc 2025094) gives Class 4 screws these periods against loss of structural integrity from natural corrosion. Its conditions matter:

• •It covers the exposed head and washer system only, not the threaded shank or concealed parts (unless the cause is a manufacturing defect), and not the look of the screw: staining, discolouration and coating dulling are excluded.
• •The screws must be correctly selected for the application and environment, installed to Hobson's instructions with a screw gun at the recommended speed, not over-tightened, and used with compatible cladding and materials.
• •Hobson's remedy is replacement screws delivered to site, not labour, removal or reinstallation. The warranty is personal to the purchaser and not transferable, and non-consumer claims should be notified to Hobson in writing within 90 days of first noticing the problem (consumers within a reasonable time).
• •Hobson asks for the fasteners and surrounding surfaces to be washed down with fresh water at least every six months in C2 and C3 environments and every three months in C4 and C5, or when contamination builds up.
• •Category descriptions are indicative only; where a site sits on a boundary the higher category applies, and CX (extreme) sites are not covered without Hobson's written confirmation first. Get professional advice on your site's category (ISO 9223 and AS 4312), or ask us.
• •For C5 (very severe marine, industrial) sites Hobson does not recommend Class 4; its 2025 warranty covers only 316 bi-metal screws there.

How to fit them

1. Fit the nut setter for the size (1/4 inch for #8-15, 5/16 inch for #10-12) in a cordless screwdriver set at no more than 2,500 RPM. Hobson does not recommend impact drivers for these screws.
2. Hold the laps together and place the screw on the lap.
3. Keep consistently firm pressure on the driver while the needle point drills through.
4. Stop as soon as the head pulls the sheets together and the seal is snug. Take care not to over-tighten: Hobson warns against it, its warranty excludes over-tightened screws, and thin sheet strips easily.
5. Sweep the metal swarf off the sheet when you finish, before it rusts and stains the surface.

Sealed hex washer needle screws in Adelaide

Allmat supplies needle point screws with seal, roofing screws, tek screws and nut setters to roofers, cladders, shed builders and trade across Adelaide and South Australia. Add the screws and the nut setter to a quote with the rest of your roofing list, and we will price the lot.

Questions