Metallics TEKD175 8 x 1/2 in. 1/4 Indented Hex Head Self-Drilling & Tapping Screws with Washer - #2 Drill Point - Steel Zinc - Each

The Metallics TEKD175 carries a #2 drill point rated for panel thickness of 0.035 to 0.100 inch. That covers typical light-gauge steel studs, strut, duct and enclosure flanges. Thicker steel than 0.100 inch needs a heavier drill point, and material thinner than 0.035 inch tends to spin out rather than tap cleanly.

No pilot hole. It's a Type BSD self-drilling and tapping screw, so the drill point cuts the hole and the thread taps it in one pass. Drill time runs about 2.5 seconds through a 1 mm thick plate.

A 1/2 inch length is sized for attaching into a single light-gauge member, with 18 threads per inch on a #8 diameter. Once you add the thickness of what you are fastening through, you need enough point and thread left to drill and tap the base metal, so stacked layers or thicker assemblies call for a longer screw in the same series rather than this one.

A 1/4 inch hex driver or nutsetter. The head measures 0.244 to 0.250 inch across the flats, 0.272 across the corners, with a head height of 0.096 to 0.110 inch. Drive type is hex, so there is no slot or Phillips recess to cam out of.

It is an integral washer under the indented hex head, not a separate piece to keep track of. Washer outside diameter is 0.322 to 0.348 inch and thickness is 0.019 to 0.031 inch, which spreads the bearing load over sheet metal and helps seat flush on a flange or strap.

The finish is zinc plating over a carbon steel body (AISI 1016-1024). Zinc plating is a mild indoor corrosion coating, so it suits dry interior electrical, plumbing, heating and air conditioning work. For sustained exterior exposure, coastal air or wet locations, a stainless self-drilling screw is the better call.

Dimensions are to ASME B18.6.3-2010 and the thread conforms to SAE J78-2013. Minimum torsional strength is 42 lb-in and case hardness runs Rockwell C32-40, which is what lets the point drill steel without snapping the shank.

Use the self-drilling type when the base material is steel and you do not want a second operation. The TEKD175 drills and taps in one pass through 0.035 to 0.100 inch panel. A plain sheet metal screw has no drill point and needs a pre-punched or pre-drilled hole, which makes it the choice only where the hole already exists or the substrate is too thin to tap.

The TEKD175 is flagged as both ARRA compliant and Buy American compliant in Metallics' product data. Country of origin is listed as multiple, so if your specification requires documentation of a single origin for a given lot, that is worth confirming against the shipped lot.