Metallics 440CTBE Carbon Steel Tap Bottoming Type 4-40 (1pc)

The 440CTBE cuts a 4-40 thread, meaning a #4 machine screw size with 40 threads per inch. It's the tap you reach for when you need to cut threads for a 4-40 machine screw into a device bracket, enclosure boss, or steel plate.

A bottoming tap has almost no lead chamfer, so it cuts full-depth threads right to the bottom of a blind hole. That's exactly what the 440CTBE is for. It is not a starting tap: you normally start the hole with a taper (plug) tap to get the thread aligned, then finish with the bottoming tap to carry the threads to the base of the hole. In a through hole, a bottoming tap on its own works but is harder to start square.

It's a carbon steel tap, which is intended for softer work: mild steel, aluminum, brass, and plastics. Carbon steel loses its edge fast in stainless or hardened material, so for stainless you want a high speed steel tap instead.

4-40 is the common machine screw thread on small electrical device hardware, cover plates, terminal blocks, and panel brackets. When a factory thread is stripped or a hole is unthreaded, a 4-40 bottoming tap cuts or recuts the thread so the original screw holds again instead of forcing a sheet metal screw into the part.

One tap per pack, supplied in a pouch. If you're stocking a van or a shop drawer and want a spare on hand for a snapped tap, order the quantity you need, since each pack is a single piece.

It has a square drive shank like any hand tap, so it's driven with a T-handle or straight tap wrench. Hand driving is what you want with a 4-40 tap anyway, a tap that small snaps easily under power.