AS 1721-1985

Specifies requirements for single start parallel metric screw threads having the ISO basic profile for triangular screw threads, covering the size range from 1mm diameter to 355mm diameter inclusive. Provides for a coarse pitch series, a fine pitch series and a constant pitch series, the latter intended for use in applications for which either the coarse or fine pitch series are unsuitable. Gives information on screw thread parameters, tolerances, deviations, thread classes, designation and symbols. Appendices are included giving the basis of the tabulated values, guidelines (with examples) for calculating the limits of size of untabulated screw threads and notes on the production of screw threads.

This standard specifies requirements for single start parallel metric screw threads having the ISO basic profile for triangular screw threads, covering the size range from 1 mm diameter to 355 mm diameter inclusive. The metric screw thread system comprises the following series:(a) The ISO coarse pitch series, which gives graded diameter/pitch combinations in diameters from 1 mm to 68 mm inclusive, and is predominantly intended for commercially produced threaded fasteners.(b) The ISO fine pitch series, which gives graded diameter/pitch combinations in diameters from 1 mm to 33 mm inclusive.(c) The ISO constant pitch series, which gives a series of standard pitches to be associated with diameters from 8 mm to 355 mm inclusive.The standard gives information on screw thread parameters, tolerances, deviations, thread classes, designation and symbols.Due to the methods adopted by ISO for rounding the tabulated values (see Appendix A), the values for the various parameters given in the tables are to be taken as authoritative for the application of this standard.Appendices are included giving the basis of the tabulated values, guidelines (with examples) for calculating the limits of size of untabulated screw threads and notes on the production of screw threads.NOTE: The ISO metric screw thread system, as given in this standard, does not provide for interference fit threads.

First published 1975.
Second edition 1985.
Incorporating: Amdt 1-1987.