BS ISO 6162-2:2018 Hydraulic fluid power. Flange connections with split or one-piece flange clamps and metric or inch screws Flange connectors, ports and mounting surfaces for use at a pressure of 42 MPa (420 bar), DN 13 to DN 76

Dimensions
Physical properties of materials
Imperial system
Clamped pipe connections
Hydraulic transmission systems
Hydraulic equipment
SI system (metric)
Service pressure
Clamps (mechanical)
Flanges
Hose connectors
Flanged fittings
Screws (bolts)
Seals
Pipe fittings
Dimensional tolerances

Link: BS ISO 6162-2:2018 Hydraulic fluid power. Flange connections with split or one-piece flange clamps and metric or inch screws Flange connectors, ports and mounting surfaces for use at a pressure of 42 MPa (420 bar), DN 13 to DN 76
Source: BSI Standards