For a Unified thread with depth 0.05 in and major diameter 0.90 in, what is the undercut finish diameter?

For a Unified thread with depth 0.05 in and major diameter 0.90 in, what is the undercut finish diameter?

• A. 0.80 in
• B. 0.85 in
• C. 0.90 in
• D. 0.70 in

Answer: (A)

In threading, the major diameter is the outermost size of the thread, and the thread depth is how far the thread profile cuts into the part measured radially from crest to root. When an undercut is added, material is removed on both sides of the thread, so the diameter at the bottom of the undercut is reduced by twice the thread depth. With a major diameter of 0.90 in and a thread depth of 0.05 in, the undercut finish diameter is 0.90 minus 2 times 0.05, which equals 0.80 in.

In threading, the major diameter is the outermost size of the thread, and the thread depth is how far the thread profile cuts into the part measured radially from crest to root. When an undercut is added, material is removed on both sides of the thread, so the diameter at the bottom of the undercut is reduced by twice the thread depth.

With a major diameter of 0.90 in and a thread depth of 0.05 in, the undercut finish diameter is 0.90 minus 2 times 0.05, which equals 0.80 in.