What type of tap is best to start cutting a thread in a piece of metal?

When starting to cut a thread in a piece of metal, the taper tap is the most effective choice. This type of tap has a tapered lead that allows for easier entry into the hole, gradually introducing the cutting edges rather than starting with a full-sized cutting surface. The tapered design helps to guide the tap more smoothly into the pre-drilled hole, reducing the risk of cross-threading or damaging the surrounding material.

Taper taps can initiate the threading process without requiring excessive force and help ensure that the thread cut is well-aligned. This feature is particularly important in metalworking, where precision in thread cutting is critical for the strength and functionality of the threaded components.

Other types of taps, such as plug taps and bottoming taps, are designed for specific purposes once a thread has already been initiated. Plug taps are used to continue cutting deeper threads, while bottoming taps are used to create threads very close to the bottom of a hole, but they lack the gradual taper that makes the taper tap ideal for starting the threading process.