Metallics JDS152SS 8 x 1/2 in. 1/4 Indented Hex Head Slotted Sharp Point Tapping Screws - 18-8 Stainless - Each

Type A is a sheet metal tapping screw with a gimlet (sharp) point that forms its own thread as it drives, so it goes into a pilot hole in sheet metal, sheet steel enclosures, and similar thin stock without a tapped hole. The JDS152SS runs 15 threads per inch at a #8 diameter, 1/2 inch length. It is not a machine screw and will not thread into a pre-tapped hole reliably.

Use caution. The JDS152SS is 18-8 stainless, and fastening stainless parts to aluminum or steel can set up a galvanic couple in some environments, which corrodes the softer metal at the joint. Outdoors or in wet or coastal locations, isolate the joint or pick a fastener that matches the base metal. In dry indoor electrical work it is generally not an issue.

Head geometry follows ASME B18.6.3-2010 and the thread follows ASME B18.6.4. One caveat from the manufacturer: dimensions for #9 diameter are independent of ASME B18.6.4. The screws are also flagged ARRA compliant and Buy American compliant, which matters on federally funded work.

Either works. The head is an indented hex with a slotted drive, so a 1/4 inch nut driver or socket seats on the hex and a flat blade fits the slot for tight spots or final snugging. Head width measures 0.244 to 0.25 in. across flats with 0.272 across corners, and the slot is 0.045 to 0.054 wide by 0.052 to 0.066 deep.

They ship in a jar of 100, which is the order minimum. Jar weight is listed at 0.38 lbs. Other sizes and quantities are available by request.

The indented hex head has an integral washer face, with an outside diameter of 0.322 to 0.348 in. and a thickness of 0.019 to 0.031 in. That spreads the bearing load a bit wider than a plain hex head, which helps on thin sheet and on slotted or oversized holes in a panel.

Head height runs 0.096 to 0.11 in., so just over a tenth of an inch of profile above the panel plus the washer face. That is low enough to clear most cover plates and trim, but it is a projecting hex head, not a flush or countersunk screw, so it will not sit flat in a chamfered hole.