Metallics TRM102M 1/4-20 x 1-1/4 in. Round Head Tri-Drive Machine Screws - Steel Zinc - Each

The TRM102M round head takes a flat blade, a Phillips bit, or a square drive. That tri-drive head is handy on service work where you only have one driver in your pouch, and it gives you a second option if one recess starts to cam out.

It is a 1/4-20 machine screw, 1-1/4 inches long. The 20 threads per inch coarse UNC pitch means it mates with standard 1/4-20 tapped holes and 1/4-20 nuts, so it will thread into a 1/4-20 strut nut, channel nut, or tapped box boss.

The TRM102M is steel with a zinc plating, which is a mild corrosion coating meant for dry indoor use. In wet, damp, or exterior locations, or anywhere with chemical washdown or coastal salt air, go to a stainless screw instead. Zinc plated steel will bloom white rust and then red rust once the coating is breached.

Round head means the screw stands proud of the surface with a domed crown and a flat bearing face underneath. It is not a flush fastener. If you need the head level with the material you want a flat head in a countersunk hole; if you need maximum bearing area against sheet metal, a truss or pan head spreads wider than this round head does.

Machine screws like the TRM102M do not self-tap. You need an existing 1/4-20 tapped hole, a 1/4-20 nut, or a channel/strut nut on the back side. For electrical work that usually means a factory-tapped enclosure hole, a ground lug, or Unistrut hardware. If you are fastening into bare sheet metal with no nut, you want a self-drilling or sheet metal screw instead.

On the TRM102M the 1-1/4 inch length is measured from under the round head to the tip, so the full 1-1/4 inches is available for material thickness plus thread engagement. Subtract your panel or strut thickness to see how much thread lands in the nut. Rule of thumb for a 1/4-20, you want at least a quarter inch of engagement, so it covers stacks up to roughly an inch.

Yes, the TRM102M is domestically made, which matters on federal, military, and other Buy American specified projects where fasteners have to be documented.

Metallics part number TRM102M is the one. It is a single model with no finish or size options to pick, so the part number alone identifies the 1/4-20 by 1-1/4 inch round head tri-drive in zinc plated steel.