A custom bolt-like part needs to be particularly straight. Can a geometric straightness tolerance be added on the threaded part of the bolt or can it only be added before threading? The example can be seen in the added picture.
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$\begingroup$ Threading has some inherent straightness tolerances in that sually the "nut" that it screws into is tapped slightly wider than the "bolt." The bolt is held with tension against the threads, and the resulting friction. Main reason for a tolerance before cutting thread is to fit it to tooling (a die or lathe). A cut thread is produced both by material removal and forming from pressures of the tool. This forming part is what may make it difficult to hold straightness (thread relative to thread). Instead consider specifying an envelope from centerline within which the threads must reside. $\endgroup$– AbelMay 15 at 13:32
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2$\begingroup$ Things like leadscrews do have a straightness tolerance. What is the purpose of the straightness? I think you normally augment straightness with shafts or pins if you can since it's a lot easier to both manufacture and verify their straightness, but sometimes you can't. It's like with gears: a gear's pitch diameter could be perfectly round and not measure round from the circumference since what matters is the tooth contact point, not the peak. A screw could similarly be straight at the core with threads of inconsistent height and work just fine. $\endgroup$– DKNguyenMay 15 at 14:38
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