The major diameter is defined as the distance between which features on an external thread?

The major diameter is defined as the distance between which features on an external thread?

• A. Crests
• B. Roots
• C. Bases
• D. Flanks

Answer: (A)

The major diameter is the largest size of an external thread, measured across its outermost points. On an external thread, those outermost points are the crests, so you determine the major diameter by measuring from crest to crest around the thread. This makes sense because the crests define the true outer boundary of the thread and set the maximum diameter that will engage with a mating part. For context, the minor diameter is measured across the roots (the bottoms of the grooves), and the pitch diameter sits between them at roughly the thread’s mid-depth, guiding fit with the mating thread. Flanks are the sides of the thread between crest and root, but the major diameter specifically uses the crests.

The major diameter is the largest size of an external thread, measured across its outermost points. On an external thread, those outermost points are the crests, so you determine the major diameter by measuring from crest to crest around the thread. This makes sense because the crests define the true outer boundary of the thread and set the maximum diameter that will engage with a mating part. For context, the minor diameter is measured across the roots (the bottoms of the grooves), and the pitch diameter sits between them at roughly the thread’s mid-depth, guiding fit with the mating thread. Flanks are the sides of the thread between crest and root, but the major diameter specifically uses the crests.