Metallics JDSP171 12 x 1 in. 5/16 Hex Head Phillips Sharp Point Tapping Screws - Steel Zinc - Each

Either works. The head is a 5/16 hex measuring 0.305 to 0.312 in. across, so a 5/16 nut driver or socket fits it, and the head also carries a Phillips recess that takes a #3 driver. That combination is handy overhead or in a panel where a hex driver holds the screw but a Phillips is the only thing that fits the space.

The JDSP171 is carbon steel with a zinc plated finish. Zinc plating is a mild indoor corrosion coating, fine for dry interior electrical work, panels, boxes, and strut. For exterior, wet, or coastal exposure, or any contact with treated lumber, specify a stainless or hot dip galvanized fastener instead, since plated zinc will bleed rust in those conditions.

Metallics lists the JDSP171 as both ARRA compliant and Buy American compliant, with country of origin China. If your specification requires domestic melt and manufacture rather than ARRA-level compliance, confirm which standard the project is written to before you submit them.

Use a #3 Phillips. The recess diameter is 0.247 in. with a gaging depth of 0.127 to 0.152 in., which is sized for a #3 tip. A #2 bit sits shallow in that recess and will cam out and chew the head, especially at the 83 lb-in torque this screw can take.

The Metallics JDSP171 is a Type A tapping screw with a gimlet (sharp) point, so it cuts its own thread into thin sheet metal, drywall backing, or a pre-punched hole without needing a tapped thread. At 11 threads per inch it is a coarse thread meant for thin-gauge material. If you are fastening into heavier steel with no pilot hole, a self-drilling point screw is the right choice instead, since a gimlet point will not drill through thick stock.

Yes, the head has an integral washer with an outside diameter of 0.398 to 0.432 in. and a thickness of 0.022 to 0.039 in. The head itself stands 0.139 to 0.155 in. high. The washer spreads the clamp load, so you do not need to add a separate flat washer when fastening through thin sheet or a slotted bracket.

Fastener length is 1 inch measured under the head, and that full inch is threaded on a Type A screw. Allow enough length past the joint for several threads to engage, so with a 1 inch screw you are realistically fastening through material up to about half its length and threading into the base behind it. For deeper stack-ups you need a longer length in the same JDSP series.

Torsional strength is 83 lb-in minimum, with the steel heat treated to Rockwell C28-38 per AISI 1016-1024 material. That is enough for normal powered driving in sheet metal, but an impact driver can exceed 83 lb-in once the screw bottoms out, so set a clutch or back off the trigger at seating. Over-torquing is the usual cause of twisted-off tapping screws.

Head dimensions follow ASME B18.6.3-2013 and the thread follows ASME B18.6.4, the tapping screw thread standard. Material is AISI 1016-1024 carbon steel. One caveat from the manufacturer: dimensions for the #9 diameter are independent of ASME B18.6.4, though that does not affect this #12 diameter screw.

They ship in a jar of 100, which is the order minimum (100 count). The jar weighs 1.02 lbs. Metallics notes that other sizes and quantities are available by request, so a different diameter or length in the JDSP series can be quoted.