Metallics JDSP181 10 x 3/4 in. 5/16 Hex Head Phillips Sharp Point Tapping Screws - Steel Zinc - Each

Either works. The JDSP181 has a 5/16 hex washer head measuring 0.305 to 0.312 in. across, so a 5/16 nut driver or socket seats on it, and the head is also Phillips recessed for a #2 Phillips bit. Head height runs 0.105 to 0.120 in. and the integral washer is 0.384 to 0.414 in. OD, 0.019 to 0.031 in. thick, so it bears on sheet metal without a separate washer. Torsional strength is 48 lb-in minimum, so keep an impact driver off it if you want to avoid snapping heads.

No pilot hole is needed in thin sheet metal. The JDSP181 is a Type A tapping screw with a gimlet (sharp) point, which pierces and forms its own thread in light gauge steel, sheet metal boxes, and wood. It is not a self-drilling screw with a drill flute, so for heavier gauge stock or structural steel you still want a pilot hole. Thread count is 12 per inch, the coarse spacing Type A uses for sheet work.

Treat it as an interior or protected fastener. It is carbon steel with a zinc plated finish, which handles indoor humidity and incidental moisture but is not stainless and is not intended for sustained exterior exposure or corrosive environments. For wet locations, specify a stainless steel tapping screw instead.

The JDSP181 is flagged compliant for both ARRA and Buy American in the manufacturer's data, with country of origin listed as China. If your specification requires domestic melt and manufacture rather than ARRA/Buy American program compliance, verify against the exact clause in your contract documents.

Head geometry follows ASME B18.6.3-2013 and the threads follow ASME B18.6.4, the tapping screw thread standard. Steel is AISI 1016 to 1024 with a case hardness of Rockwell C28-38. Those are the figures to hand an inspector asking what the fastener conforms to.

At 3/4 in. of length under a #10 diameter, the JDSP181 gives you enough thread for sheet metal, box flanges, strap, and light gauge stud work where total grip is thin. If you are stacking material or fastening through a thicker substrate, step up in length; this one is sized for shallow engagement. Metallics builds the JDSP series in other diameters and lengths by request.

They come in a jar of 100, and 100 count is the order minimum. The packed jar weighs 0.63 lbs. Handy for a van stock item rather than a loose bin count.

The Phillips recess is 0.178 in. diameter with a gaging depth of 0.102 to 0.127 in., which is a #2 Phillips. A #1 bit will cam out and a #3 will not bottom in the recess, so stock #2 bits for these.