Metallics 3416CTB Carbon Steel Tap Bottoming Type 3/4-16 (1pc)

The 3416CTB cuts a 3/4-16 thread, meaning 3/4 inch nominal diameter at 16 threads per inch. That is a UNF (fine) pitch, not the coarse 3/4-10 UNC you would find on standard coarse-thread bolts, so match the fastener pitch before you cut. It comes as a single tap, packed in a pouch.

A bottoming tap is for finishing threads to the bottom of a blind hole. It has almost no tapered lead, usually a chamfer of about one to one and a half threads, so it will thread nearly the full depth of a closed hole. That same lack of taper makes it hard to start squarely in a fresh hole, so run a taper or plug tap first, then follow with the 3416CTB to bring the threads down to the base. For a through hole you generally do not need it at all.

Carbon steel. It is intended for hand tapping and chasing threads in mild steel, aluminum, and other softer materials, typically with a tap wrench rather than a powered machine. If you are production tapping or cutting into stainless or hardened stock, a high speed steel tap is the right choice instead.

Yes, chasing a damaged or paint-filled 3/4-16 female thread is one of the common uses for this tap, and the bottoming form lets you run it to the base of a closed boss where a taper tap would stop short. It is stocked as an electrical supply item for exactly that kind of field repair. Thread size and pitch have to match at 3/4-16, so verify the existing thread with a pitch gauge first.

One tap per pouch, and it is the bottoming type only. No taper or plug tap is included, so if you are cutting a new 3/4-16 blind hole you will need to order those separately to start the thread. A tap wrench or T-handle is also not included.

Order it as Metallics 3416CTB. The number reads out as the spec: 3/4-16 thread, carbon steel, tap, bottoming. Metallics uses the same pattern across the family, so the taper and plug versions of the same thread differ only in that last letter group.