It is usually a bolt on an enclosure tied to an electric potential within the enclosure, supporting the connection of a cable.
Cable Dia for wire size& Fixed hole diameter
cable dia(mm) | 14.30 | 13.0 | 11.8 | 10.4 | 9.1 | 8.8 | 7.1 | 11.8 | 10.5 | 9.1 | 8.8 | 7.5 | 6.0 | 4.9 | 8.3 | 7.4 | 5.9 | 5.4 |
fixed hole dia(mm) | 13.50 | 10.50 | 8.5 | 7.0 | 5.5 |