![]() ![]() ![]() diameter specification is usually by the nominal thickness of the male screw some series however use confusing notation where stated diameter does not equal real diameter.the smaller angle the deeper thread for the same pitch - Whitworth with 55° is deeper than unified/metric with 60°, 47.5° BA is deeper than equivalent Whitworth.the finer pitch, the smaller depth but the tighter tolerances are needed on maintaining the diameter.manual tools like open dies from two halves allow cutting a thread of a given pitch into a range of diameters.before the age of CNC, threads were often made on a lathe using combinations of gears to achieve a ratio between rotation of workpiece and translation of tool.UNS this allows more variability while providing at least some off-the-shelf availability of taps/dies or a selected subset can comprise a "series" of their own, eg.the nonstandards can be completely ad-hoc.forms can be used for nonstandard diameter/pitch combination.series often have primary/first, secondary/second, sometimes tertiary/3rd, and sometimes "avoid if possible" choices.example is metric coarse/fine, or UNC/UNF/UNEF, or BSW/BSF, or ME.thread series belong under a thread form BSW, BSF and ME, and the pipe G and R, are all Whitworth form UNC, UNF, UNEF, UNS, UN, and the pipe NPT and NPS, are all 60-deg.thread series are sets of diameter-pitch tuples, defined for a purpose.for enclosures/lids (glass forms, buttress).for motion screws (ACME, trapezoid, buttress).1/4-20 for camera tripods) or may be insufficient strength (eg. Whitworth and Unified have limited compatibility, where the pitch/diameter fits they may screw together may be good enough (eg.sometimes threads of different forms can be deceptively compatible increased force (and even stripping) may be needed, or the fit may be too loose, or joint strength may be compromised.JIS metric thread hole strips more readily with ISO metric screw than ISO metric thread hole tolerances - these can introduce subtle differences between otherwise identical standards, eg.multistart threads have lead (distance the screw travels on single turn) equal pitch times number of starts common on faster leadscrews, enclosure lids/caps, and some self-tapping screws.most threads are single-start, forming a single helix here the pitch equals the lead.most common is right-handed thread, RH, considered default when not specified explicitly LH or left stands for left-handed thread, usually used where direction of rotation would tend to unscrew RH.pipe threads often exist in straight and tapered forms - BSPP vs BSPT/BSPTr (G vs R), NPS vs NPT.flat crest/root are more friendly to manufacture, cheaper, the edges can accommodate some rounding of the tools by wear.flat crest, round root for UNJ and MJ forms, "flavors" of standards.flat for metric and US and for translation screws, for truncated Whitworth for fasteners the root is usually slightly round or radiused to avoid stress concentration.crest/root forms (flat and how wide, or round and with what radius). ![]() for translation screws, 29° for ASME, 30° for trapezoid, 60° for truncated 60°.typically 60° for metric and US series, 55° for Whitworth, 47.5° for BA.Thread form defines the shape of the thread: UNC,UNF,UNEF,UNS: like metric, but dia/pitch imperialīSF: British Standard Fine, like Whitworth but finer pitchīSC: British Standard Cycle, CEI Thread angle 60°, fine pitch, 1/4" and above all at 26 tpi, or 20 tpi ("CEI20")īSP,G,R: British Standard Pipe, like Whitworth but for pipe diameters, dia for inner pipe dia! TABLE OF DIMENSIONS, STANDARDS AND EXAMPLES Conference for unification report, vol.73, small screws: ![]()
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