The thread specification 3/8'' - 24UNF 2B x 1-1/2'' indicates a diameter of 3/8 inch, a thread length of 1-1/2 inches, and a fine thread pitch of 24 threads per inch. The "2B" designation specifies medium tolerance for internal threads, with "B" indicating internal and "A" for external threads. This standard is part of the Unified Thread Standard, which governs thread specifications in the United States.
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If this is a bolt, the 1-1/2" is the length from under the head to the tip of the bolt. It includes the shank. If this is a thread call out on a drawing, it means the thread is 1-1/2" long. You need to specify where you're seeing this call out.eurekameh said:What does the thread note 3/8'' - 24UNF 2B x 1-1/2'' mean? I know that the diameter of the thread is 3/8'', but what's the 1-1/2''? Is that the length of the thread?