Threading Tables

Chart No 15 - British Standard Worm Threads

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This thread is similar in form to the Acme Thread, in that the included angle is 29 degrees, but the depth of the thread is greater. The width of the flat at both top and bottom are therefore different. The table below gives full machining details.

Worm Threads (29 Deg Thread Angle) - NOT Acme Dimensions in Inches except where stated
Thread Form Data
T.P.I.	Pitch	Addendum	Thread Depth below pitch line	Total Thread Depth	Tooth Thickness at pitch line	Top Thread Width	Bottom Thread Width
1	1.000	0.3183	0.3683	0.6866	0.5000	0.3354	0.3100
1½	0.6677	0.2122	0.2455	0.4577	0.3333	0.2236	0.2066
2	0.5000	0.1592	0.1841	0.3433	0.2500	0.1677	0.1550
2½	0.4000	0.1273	0.1473	0.2746	0.2000	0.1341	0.1240
3	0.3333	0.1061	0.1228	0.2289	0.1667	0.1118	0.1033
3½	0.2857	0.0909	0.1053	0.1962	0.1429	0.0958	0.0886
4	0.2500	0.0796	0.0920	0.1716	0.1250	0.0838	0.0775
4½	0.2222	0.0707	0.0818	0.1526	0.1111	0.0745	0.0689
5	0.2000	0.0637	0.0736	0.1373	0.1000	0.0670	0.0620
6	0.1667	0.0531	0.0613	0.1144	0.0833	0.0559	0.0516
7	0.1429	0.0455	0.0526	0.0981	0.0714	0.0479	0.0443
8	0.1250	0.0398	0.0460	0.0858	0.0625	0.0419	0.0387
9	0.1111	0.0354	0.0409	0.0763	0.0556	0.0373	0.0344
10	0.1000	0.0318	0.0369	0.0687	0.0500	0.0335	0.0310
12	0.0833	0.0265	0.0307	0.0572	0.0416	0.0279	0.0258
14	0.0714	0.0227	0.0263	0.0490	0.0357	0.0239	0.0221
16	0.0625	0.0199	0.0230	0.0429	0.0312	0.0209	0.0194
18	0.0556	0.0177	0.0205	0.0382	0.0278	0.0186	0.0172

NOTES:- Depth of Thread = 0.6866 X Pitch
Width at Top of Thread = 0.335 X Pitch
Width of Space at Bottom of Thread = 0.310 X Pitch
Width of Thread at Pitch Line = 0.5 X Pitch
Addendum = 0.3194 X Pitch

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