Metallics TRM99M 1/4-20 x 1/2 in. Round Head Tri-Drive Machine Screws - Steel Zinc - Each

The TRM99M round head screw takes three different drivers: slotted, Phillips, or square. Whichever of those is already on your belt will seat it, which is the point of a tri-drive head on service work where you are not carrying a full driver set.

The TRM99M is a 1/4-20 machine screw, which is the common thread for 1/4 inch strut nuts, channel inserts, and threaded hardware on electrical enclosures. It is a machine thread, so it needs a tapped hole or a mating nut, not wood or sheet metal on its own. At 1/2 inch of length you get roughly enough thread for a nut plus one layer of light material, so check your total stack before ordering.

Zinc plated steel, which is what the TRM99M is made from, is a mild corrosion coating meant for dry interior service. For wet, washdown, coastal, or buried locations, step up to a stainless 1/4-20 machine screw instead; zinc will eventually bloom and seize in those conditions.

A round head sits on top of the surface and needs no countersink, so it works on thin sheet steel enclosure walls and flat brackets where a flat head would have nothing to seat into. If your part is already countersunk, a round head will not sit flush and you want a flat head instead.

Yes, the TRM99M 1/4-20 x 1/2 in. round head screws are domestically made, which matters if you are filling a government or institutional order carrying a domestic-content requirement.

Order the Metallics TRM99M. That one number covers the 1/4-20 x 1/2 inch round head tri-drive screw in zinc plated steel, so there is no finish or drive suffix to specify.