Metallics TSF21V 8 x 1 in. Flat Head Phillips Tapping Screws - Steel Zinc - Each

It will if the countersink matches a standard #8 flat head. The head on the TSF21V runs 0.285 to 0.312 in. across with a head height of 0.084 to 0.1 in., so an 82 degree countersink cut for a #8 flat head takes it flush. If the plate or strap you are fastening has only a plain drilled hole with no countersink, the head will stand proud and you want a pan or hex washer head instead.

Yes. The TSF21V is made to ASME B18.6.4-1998 for dimensions and threads, with steel per AISI 1016-1024. Metallics flags it ARRA compliant and Buy American compliant, with country of origin listed as multiple. Note that the published dimensions for #9 diameter screws in this family are independent of ASME B18.6.4, but the #8 x 1 in. is covered.

No. The TSF21V is a Type A tapping screw with a coarse 15 TPI sheet metal thread and a gimlet point, meant to cut its own thread in unthreaded sheet metal. It will not mate with the pre-tapped 8-32 or 10-32 holes in a box, plate ear, or ground lug. For those, use machine screws in the matching machine thread.

A #2 Phillips bit. The recess on the TSF21V measures 0.182 in. diameter, 0.11 in. deep, with a 0.03 in. slot width, which is standard #2 Phillips geometry. One bit covers the whole jar, so there is no mixing drivers on the job.

These ship in a jar of 500, which is the order minimum for the TSF21V. The jar weighs 2.1 lbs and measures 3 x 3 x 4.57 in., so it stores easily on a van shelf or in a gang box. Metallics notes other sizes and quantities are available by request.

The TSF21V is case hardened to Rockwell C28-38 with a minimum torsional strength of 39 lb-in. That is enough to self-tap sheet metal, but it is a tapping screw, not a self-drilling screw, so you still need a pilot hole in heavier gauge material. Driving on high torque with an impact is the usual way these shear or cam out the Phillips recess.

Work off the gaging diameter of 0.267 in. on the TSF21V, which is the thread crest reference. The pilot has to be smaller than the thread so the screw forms its own thread as it goes, and in thin sheet the gimlet point will start on its own with little or no pilot. Match the pilot to your material gauge, going larger as stock gets thicker.

These are zinc plated carbon steel, which is a mild corrosion coating for dry interior work: panel interiors, device plates, duct, indoor strut and strap mounting. For exterior, wet, or coastal exposure, zinc plating will eventually rust through and stainless or hot dip galvanized fasteners are the right call.