Metallics TEKD16M 8 x 5/8 in. 1/4 Indented Hex Head Self-Drilling & Tapping Screws with Washer - #2 Drill Point - Steel Zinc - Each

It is a #8 diameter UNC thread at 18 threads per inch, 5/8 inch long, built to SAE J78-2013 for thread form and ASME B18.6.3-2010 for dimensions. At 18 TPI the thread engages well in sheet in the 0.035 to 0.100 inch range, which includes 18 gauge steel. With 5/8 inch of length, keep total stack-up thin enough that several threads pass through the back of the panel.

Use a 1/4 inch hex driver or nut setter. The indented hex head measures 0.244 to 0.25 inch across the flats and 0.272 inch across the corners, so a standard 1/4 inch magnetic nut setter in a drill or impact driver seats it correctly. Head height runs 0.096 to 0.11 inch.

An integral washer is part of the head, with an outside diameter of 0.322 to 0.348 inch and a thickness of 0.019 to 0.031 inch. That bearing surface spreads the clamp load on thin sheet and helps seat flat against strut, panel, or bracket without dimpling. No separate washer needs to be ordered.

They ship in a jar with a 1,000 piece order minimum. Package weight is listed at 3.84 lbs. If you need a different count or a different size in the same hex washer head self-drilling family, Metallics makes other sizes and quantities available by request.

The TEKD16M is steel with a zinc finish, which is a dry-interior plating. It is well suited to indoor conduit strap, panel, and bracket work. For wet, coastal, or corrosive locations, specify a stainless self-drilling screw instead, since zinc plate will eventually rust in standing moisture.

Metallics lists this screw as Buy American compliant and ARRA compliant. Country of origin is recorded as multiple, so if your specification requires a single documented source country, get the certification for the specific lot before submitting.

Minimum torsional strength is 42 lb-in, with the screw heat treated to Rockwell C32-40. Set your impact or drill clutch below that. Metallics notes minimum torques are the same for stainless and steel self-drill screws, and drill time runs about 2.5 seconds through a 1 mm plate.

The TEKD16M is made from AISI 1016 to 1024 carbon steel, case hardened to Rockwell C32-40. That combination gives a hard enough point to cut sheet steel while leaving the core tough enough to resist snapping at the 42 lb-in minimum torsional rating.