Metallics JTSS81SS 10 x 3 in. Pan Head Square Drive Tapping Screws - 18-8 Stainless - Each

A #2 square (Robertson) bit drives these. The recess is spec'd as driver size 2R, measuring 0.112 in. across the flats with a 0.060 to 0.075 in. penetration gaging depth. The recess has a square center opening, slightly tapered side walls and a conical bottom, so a worn or undersized bit will cam out. Rated torsional strength is 48 lb-in minimum.

You can, but watch the dissimilar metal issue. Fastening 18-8 stainless parts to aluminum or steel can set up a galvanic couple and corrode in some environments, particularly wet or coastal exposure. For an all-steel assembly in a dry interior, a plated carbon steel tapping screw avoids the problem entirely. Where you need the corrosion resistance of stainless in the fastener itself, isolate or seal the joint.

The JTSS81SS is a Type A tapping screw with a gimlet point, so it needs a pilot hole in metal, it will not drill its own. The sharp gimlet point lets it start in thin sheet, wood and soft materials without a pilot in many cases, but in gauge steel you drill first. If you want to skip the pilot hole in steel, you want a self-drilling (Type AB or TEK style) screw instead.

It is a #10 by 3 in. screw with 12 threads per inch, made to the ASME B18.6.4 thread standard. The 3 in. length gives you real purchase through furring, strut backing or stacked material, and the 12 TPI coarse thread is what holds in sheet metal and soft substrate rather than in a tapped machine thread.

Metallics lists the JTSS81SS as ARRA compliant and Buy American compliant, with country of origin China. Procurement officers on federally funded work should check which of those designations their specific contract clause calls for, since the two programs treat fasteners differently.

18-8 stainless is the standard austenitic grade for general corrosion resistance, so it handles exterior exposure, washdown areas and damp mechanical spaces far better than a zinc plated screw. In heavy chloride or coastal salt spray, 316 is the step up. The one caution with stainless here is contact with aluminum or steel, which can create a galvanic couple in some environments.

They ship in a jar of 100, and 100 count is the order minimum. Shipping unit weight is 1.82 lbs. The jar format is practical on a service truck, it reseals and keeps a long #10 from scattering in a gang box. Other sizes and quantities are available by request.