Metallics TP143SBC Screws 1/2-13 x 2-1/2 Btn Hx Pin TR M (100 pcs)

The TP143SBC is a 1/2-13 x 2-1/2 inch screw. That 1/2-13 callout is the standard UNC coarse machine thread, so it mates with a 1/2-13 tapped hole or a standard 1/2-13 nut, and the 2-1/2 inch length is measured on the shank under the button head. Count your total grip (material thickness plus washer and nut) against that 2-1/2 inches before ordering.

A pin-in-hex key, not a plain Allen wrench. The TP143SBC has a hex socket with a solid pin standing up in the center, so a standard hex key bottoms out on the pin and will not seat. You need a pin-in-hex (pin-in-socket) driver bit or key sized to the socket, and that is what makes the fastener tamper resistant: it will not come out with a tool off a common hex key set.

They ship 100 pieces to the pack. For a security or MRO job that is usually enough to do a run of enclosure covers, grates, or panel fastening in one order, and it keeps every fastener on the install taking the same pin drive key.

Button head is the lowest-profile option of the common socket heads, with a wide shallow dome rather than a tall cylindrical cap. On the TP143SBC that gives a broader bearing surface against the part and less height above it than a socket cap head of the same 1/2-13 thread, which is why it gets used on covers, guards, and grates where a tall head would catch. It is not flush, though. If you need the head fully recessed, you want a flat (countersunk) head in a countersunk hole instead.

Tamper resistance is the whole point of the pin drive on the TP143SBC. Anyone with a common hex key set can back out a standard socket screw; a pin-in-hex head cannot be driven without the matching pin key. That matters on public-facing work: utility and electrical enclosure covers, equipment guards, transit and park fixtures, restroom partitions and anywhere a panel needs to stay closed. Keep one or two of the matching pin drivers with the maintenance tools, because the same feature that stops a stranger also stops your own crew without the right bit.

Order it as Metallics TP143SBC. That one number covers the complete item: 1/2-13 x 2-1/2 inch, button head, hex pin tamper-resistant drive, 100 pieces per pack. If you are matching fasteners already installed on a job, confirm the drive is a pin-in-hex and the thread is 1/2-13 coarse, since a 1/2-20 fine thread screw of the same length will not start in the same hole.

Either works. It is a machine screw thread, 1/2-13, so it can thread into a 1/2-13 tapped hole in the panel or frame, or pass through a clearance hole and take a 1/2-13 nut on the back. The tapped-hole approach is what you want on a cover that gets removed, since there is no loose nut to lose behind the panel, and it keeps the tamper resistance meaningful because there is nothing accessible on the blind side.