ISO 12129-1:2019 specifies a system of fits applicable to metallic plain bearings used in general engineering for mean relative bearing clearances, ψm, of 0,56 up to 3,15. Other clearance ranges can be used depending upon the requirements in specific applications.

This system of fits is not applicable to half-bearings and bushes which, due to their special characteristics, are not measured by diameter but by wall thickness, and which are dimensionally changed on assembly. It is not applicable to profile bore or tilting pad bearings, or to cases where specific tolerances have been established by consideration of the bearing performance at both extremes of clearance.

This document is applicable preferably to rotating machine parts and shafting, but it can be used similarly in other ranges of application.