The pin diameters actually used may be based on any standard series for sizes of bar material provided that the intervals between adjacent sizes do not exceed the R20 Interval (1.12) The next size above the minimum pin diameter, D min as given in the above table should be used. The Nominal diameter D used is then subject to the tolerances specified in 5.2 of IS:6132 (Part I). 1971 The eye outside diameter then becomes twice the nominal Pin Diameter D subject to the tolerances in 5.2 of IS:6132 (Part II) - 1971. Specification for Shackles : Part I General Requirement for grade 30, 40, and 63 only. Shackles of Grade 30, 40, 63 confirm to I.S.I specification 6132