This Standard contains general metric standards for a 60 deg. symmetrical screw thread with a basic ISO 68 profile designated M profile. The M profile threads of tolerance class 6H/6G are intended for metric applications where inch class 2A/2B have been used. At the minimum material limits, the 6H/6G results in a looser fit than the 2A/2B. Tabular data is also provided for a tighter tolerance fit external thread of class 4G/6G which is approximately equivalent to the inch class 3A but with an allowance applied. Formulation and tolerancing data is included for applications requiring other fits.