Metallics JTSS10SS 8 x 1-1/4 in. Pan Head Square Drive Tapping Screws - 18-8 Stainless - Each

A #2 square (Robertson) bit. The recess is specified as driver size 2R, measuring 0.112 inch across the flats with a gaging depth of 0.060 to 0.075 inch, so a standard #2 square bit seats fully. The recess has a square center opening with slightly tapered side walls and a conical bottom.

The JTSS10SS is a Type A tapping screw with a gimlet point, so the point is sharp and tapered and will start in sheet metal with only a small pilot hole. Type A thread form is coarse at 15 threads per inch, intended for thin sheet metal and similar light materials rather than thick steel plate. Thread geometry follows ASME B18.6.4.

They can. Fastening stainless steel parts to aluminum or steel creates a galvanic couple in some environments, which accelerates corrosion of the less noble metal. On an aluminum strut, box, or panel in a damp or coastal location, consider isolating the joint or using a fastener material matched to the base metal. In dry indoor work the 18-8 stainless screw is generally used as is.

Minimum torsional strength is 39 lb-in. That is the floor for a #8 18-8 stainless tapping screw, and it is low enough that a high-torque impact driver will twist heads off. Run these with a drill/driver set to a low clutch setting or finish by hand.

They ship in a jar of 100 as the order minimum, so one unit is 100 screws. Jar weight is listed at 0.68 lbs.

Head width runs 0.306 to 0.322 inch and head height 0.105 to 0.115 inch. The pan head sits proud of the surface with a flat underside bearing, so it spreads load on sheet metal but will not sit flush. If you need the head buried, you want a flat or oval head countersunk screw instead.

Head and recess dimensions conform to ASME B18.6.3-2013 and the thread form to ASME B18.6.4. Note that the material is sourced multiple-origin and Metallics lists the screw as not Buy American compliant and not ARRA compliant, which matters on federally funded work.

Metallics lists the JTSS series for the electrical, plumbing, heating and air conditioning industries, which is where #8 x 1-1/4 inch sheet metal screws get used most, duct seams, device and junction box mounting, panel and bracket attachment. The square drive resists cam-out when you are driving overhead or one handed in a ceiling.