BS 919-1:2007

• 21.040.30 Special screw threads

This part of BS 919 specifies requirements for the following types of gauges intended for use in the checking of products with unified screw threads for conformity with BS 1580.

1. Screw gauges:
   1. solid screw plug gauges, GO and NOT GO;
   2. solid screw ring gauges, GO and NOT GO;
   3. adjustable screw ring gauges, GO and NOT GO;
   4. adjustable screw calliper gauges GO and NOT GO.
2. Setting plugs for adjustable ring gauges and for calliper gauges, GO and NOT GO:
   1. double length;
   2. single length.
3. Screw check plugs for solid screw ring gauges, GO and NOT GO.
4. Plug gauges and calliper gauges for the crest diameters of product threads, GO and NOT GO.

Annex A gives information about the various types of gauges covered by BS 919. Annex B explains the conventional method for showing the tolerance zones of gauges. Guidance on the calculation of the effective diameter equivalent of pitch and angle errors is given in Annex C. Annex D recommends a method for gauging screw threads before and after coating. Notes on the setting to size of adjustable screw ring gauges are presented in Annex E, while Annex F presents a comparison of British and American screw thread terminology. Annex G discusses the tolerances for major, effective and minor diameters and flank angle and pitch permitted by BS 1580. Guidance on the hardness of gauges is given in Annex H.