SP R.20

6.1.21.1.2 If ISO 261 has been specified, the thread series shall be coarse or 3, 4, 6 or 8 pitch. Diameters shall be selected from Table 2 Column 1 of ISO 261. The threads shall be Class 6g for bolting and studs, and Class 6H for nuts. For other threads they shall be Class 6g or 4h for external threads and Class 6H or 5H for internal threads. ................
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