Metallics JSTSP38 14 x 1-1/2 in. Pan Head Phillips Tapping Screws - 18-8 Stainless - Each

That is exactly what a Type A tapping screw is for. The JSTSP38 has a gimlet point, which starts in a pilot hole and forms its own thread as it drives into sheet metal. You still drill a pilot sized to the screw's root diameter; the point does the threading, not the hole-making. The thread is 10 per inch to ASME B18.6.4.

They can. 18-8 stainless fastened to aluminum or steel forms a galvanic couple in wet or coastal environments, with the aluminum or steel as the sacrificial side. Indoors and dry it is a non-issue, which is where most electrical box and enclosure work sits. For wet exterior aluminum, isolate the joint or pick a fastener closer to the base metal in the galvanic series.

A #3 Phillips bit. The recess on the JSTSP38 runs 0.268 to 0.281 inch in diameter at 0.148 inch deep, so a #2 bit will cam out and chew the recess under load. Keep a #3 in the gun if you are running a jar of these.

125 lb-in minimum torsional strength. Stainless is softer than hardened carbon steel, so set the clutch rather than running an impact wide open, especially into heavier gauge steel where the screw is cutting thread the whole way.

The pan head measures 0.457 to 0.476 inch across and 0.156 to 0.169 inch high, built to ASME B18.6.3-2013. That bearing surface covers a clearance hole for a #14 shank comfortably, but it is not a washer head, so a slotted or badly oversized hole will need a separate flat washer.

Metallics lists the JSTSP38 as ARRA compliant and Buy American compliant. Country of origin on the record is China, so if your contract clause is a strict domestic-melt-and-manufacture requirement rather than the ARRA compliance flag, check the clause language against that origin before you submit.

They ship in a jar of 100, and 100 count is the order minimum. Figure roughly 1.84 lbs for the jar, which is useful when you are loading a van with several sizes.