In UDC 621.8 is classed information about various machine elements and installations: bearings, shafts, gears, gearing and other forms of power transmission, materials handling and transfer equipment, cranes, lifts, excavating and dredging equipment, fastening and fixing devices (including screws, bolts and associated tools), and lubrication and lubricants.
Class here information about machine elements, etc. treated generally. If they are treated as parts of specific kinds of machinery, class with the subject, adding the -1/-9 auxiliaries listed under 62.