Which diameter describes the distance between crests of an external thread?

Which diameter describes the distance between crests of an external thread?

• A. Major diameter
• B. Minor diameter
• C. Pitch diameter
• D. Root diameter

Answer: (A)

The distance across the crests of an external thread is the major diameter. This is the largest diameter of the thread, measured from crest to crest, and it defines the external size of the screw or bolt. The major diameter is what you use to specify the size of an externally threaded part because it relates to how the bolt will fit into a threaded hole or nut. Other diameters describe different features: the minor (root) diameter is the smallest diameter at the bottom of the thread, and the pitch diameter is the theoretical middle diameter where the thread thickness equals the pitch, used for calculating fit and engagement with the mating internal thread. Root diameter is another term for the smallest diameter at the thread roots.

The distance across the crests of an external thread is the major diameter. This is the largest diameter of the thread, measured from crest to crest, and it defines the external size of the screw or bolt. The major diameter is what you use to specify the size of an externally threaded part because it relates to how the bolt will fit into a threaded hole or nut. Other diameters describe different features: the minor (root) diameter is the smallest diameter at the bottom of the thread, and the pitch diameter is the theoretical middle diameter where the thread thickness equals the pitch, used for calculating fit and engagement with the mating internal thread. Root diameter is another term for the smallest diameter at the thread roots.