The stock should be tapered first to, I think, 3/4 in per foot and then threaded for male threads. For female threads, it is best to taper the bore with a specific tapered reamer first before tapping. Many do not ream first, but it increases tap load appreciably which can hurt the thread quality.
My understanding is that threading tapered threads on straight material, either male or female is NPT. Tapering the material, male or female is NPTF, or dryseal pipe threads. In my industry we used NPTF exclusively. Since we never made male fittings, our female NPTF threading always involved taper reamers.
My understanding is that threading tapered threads on straight material, either male or female is NPT. Tapering the material, male or female is NPTF, or dryseal pipe threads. In my industry we used NPTF exclusively. Since we never made male fittings, our female NPTF threading always involved taper reamers.
No. They are both tapered. NPTF and NPT threads are very nearly the same. The difference is that assembled NPT threads make full contact only along the thread flanks, which can leave a bit of a gap along the root/crest where the threads mate, so NPT needs a sealant or pipe tape to insure that the gap is definitely blocked. NPTF threads are dimensioned ever so slightly differently so that they make contact on the flanks and the root/crest simultaneously so they should seal better even dry (hence the "dryseal" moniker).
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