Threads and Threading - Sportpilot.info
Threads and Threading - Sportpilot.info
Threads and Threading - Sportpilot.info
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Machinery's H<strong>and</strong>book 27th Edition<br />
WHITWORTH THREADS 1857<br />
WHITWORTH THREADS<br />
British St<strong>and</strong>ard Whitworth (BSW) <strong>and</strong> British St<strong>and</strong>ard Fine (BSF) <strong>Threads</strong><br />
The BSW is the Coarse Thread series <strong>and</strong> the BSF is the Fine Thread series of British<br />
St<strong>and</strong>ard 84:1956—Parallel Screw <strong>Threads</strong> of Whitworth Form. The dimensions given in<br />
the tables on the following pages for the major, effective, <strong>and</strong> minor diameters are, respectively,<br />
the maximum limits of these diameters for bolts <strong>and</strong> the minimum limits for nuts.<br />
Formulas for the tolerances on these diameters are given in the table below.<br />
Whitworth St<strong>and</strong>ard Thread Form.—This thread form is used for the British St<strong>and</strong>ard<br />
Whitworth (BSW) <strong>and</strong> British St<strong>and</strong>ard Fine (BSF) screw threads. More recently, both<br />
threads have been known as parallel screw threads of Whitworth form.<br />
With st<strong>and</strong>ardization of the Unified thread, the Whitworth thread form is expected to be<br />
used only for replacements or spare parts. Tables of British St<strong>and</strong>ard Parallel Screw<br />
<strong>Threads</strong> of Whitworth Form will be found on the following pages; tolerance formulas are<br />
given in the table below. The form of the thread is shown by the diagram. If p = pitch, d =<br />
depth of thread, r = radius at crest <strong>and</strong> root, <strong>and</strong> n = number of threads per inch, then<br />
d 1<br />
⁄3 p 27 ° cot 30 ′<br />
= × = 0.640327p = 0.640327 ÷ n<br />
r = 0.137329p = 0.137329 ÷ n<br />
It is recommended that stainless steel bolts of nominal<br />
size 3 ⁄ 4 inch <strong>and</strong> below should not be made to Close Class<br />
limits but rather to Medium or Free Class limits. Nominal<br />
sizes above 3 ⁄ 4 inch should have maximum <strong>and</strong> minimum<br />
limits 0.001 inch smaller than the values obtained<br />
from the table.<br />
Tolerance Classes : Close Class bolts. Applies to screw<br />
threads requiring a fine snug fit, <strong>and</strong> should be used only for special work where refined<br />
accuracy of pitch <strong>and</strong> thread form are particularly required. Medium Class bolts <strong>and</strong> nuts.<br />
Applies to the better class of ordinary interchangeable screw threads. Free Class bolts.<br />
Applies to the majority of bolts of ordinary commercial quality. Normal Class nuts.<br />
Applies to ordinary commercial quality nuts; this class is intended for use with Medium or<br />
Free Class bolts.<br />
Table 1. Tolerance Formulas for BSW <strong>and</strong> BSF <strong>Threads</strong><br />
Class or Fit<br />
Tolerance in inchesa (+ for nuts, − for bolts)<br />
Major Dia. Effective Dia. Minor Dia.<br />
Close<br />
2<br />
⁄3T Bolts Medium T<br />
Free<br />
3<br />
⁄2T Close … 2<br />
⁄3T 0.2p + 0.004<br />
Nuts<br />
}{<br />
b<br />
Medium … T 0.2p + 0.005c Normal … 3<br />
⁄2T 0.2p + 0.007d p<br />
d<br />
r<br />
55˚<br />
r<br />
2<br />
⁄3T + 0.01 p<br />
2<br />
⁄3 T + 0.013 p<br />
T + 0.01 p<br />
T + 0.02 p<br />
3<br />
⁄2T + 0.01 p<br />
3<br />
⁄2 T + 0.02 p<br />
a The symbol T 0.002 D<br />
, where D = major diameter of thread in inches; L<br />
= length of engagement in inches; p = pitch in inches. The symbol p signifies pitch.<br />
b For 26 threads per inch <strong>and</strong> finer.<br />
c For 24 <strong>and</strong> 22 threads per inch.<br />
d For 20 threads per inch <strong>and</strong> coarser.<br />
3 = + 0.003 L + 0.005 p<br />
Copyright 2004, Industrial Press, Inc., New York, NY