Metallics TXV1278 12-24 x 7/8 in. 5/16 Hex Head Heavy Duty Drill Screws - #4 Drill Point - All-Weather - Each

It is built for it. Minimum torsional strength is 92 lb-in, hardness runs Rockwell C32-40, and the steel is AISI 1016-1024, which is why Metallics calls the TXV a heavy duty steel-to-steel screw. The 92 lb-in figure matters most on the install: it is the point at which the screw twists off, so set your impact clutch below it rather than driving on full power.

No. The TXV1278 is not Buy American compliant and is not ARRA compliant, with country of origin listed as multiple. If your contract carries a domestic sourcing clause, this part will not satisfy it and you need a certified domestic fastener instead.

Yes. The TXV1278 carries a zinc plus all-weather coating, which is what Metallics specifies for exterior and high-humidity steel-to-steel work such as rooftop strut, outdoor enclosures, and damp mechanical spaces. For direct saltwater exposure or chemical environments, stainless is the better call.

There is a bonded washer on the head, 0.398 to 0.432 in. outside diameter and 0.022 to 0.039 in. thick. That OD spreads the clamp load over slotted strut and sheet steel, and keeps the head from pulling through thinner panel. It is not a rubber EPDM roofing washer, so do not treat it as a weatherproof seal on a penetration through roofing membrane.

The TXV1278 runs 7/8 in. long at 12-24 thread, 24 threads per inch. Subtract your top member and the drill-point length, and what remains is thread engaged in the base steel. On a base panel in the 0.110 to 0.210 in. range, 7/8 in. gives room for a bracket or strut up to roughly a half inch thick and still fully tap out the back. If you are stacking thicker members, step up to a longer TXV.

Dimensions conform to ASME B18.6.3-2010 and the thread to SAE J78-2013, the self-drilling tapping screw standard. For spec-driven jobs that means head and thread geometry are interchangeable with any other screw built to those same standards.

No pilot hole needed within its rated range. It is a drill point screw, so the #4 point cuts its own hole and the 12-24 thread taps as it goes, in one pass. The limit is the 0.110 to 0.210 in. panel thickness; past that the point will burn before it penetrates and you should drill first.

They ship in a jar, with a 100 count order minimum. So the smallest buy is one 100-piece jar of TXV1278. Metallics does offer other sizes and quantities of the TXV series on request if you need a different length or a bulk box for a larger run.

Head height is 0.139 to 0.155 in., a low profile hex washer head. That matters when you are fastening behind a panel flange or under an enclosure rail where a tall head would foul the fit. Total stack above the surface is that head height plus the 0.022 to 0.039 in. washer.