ISO 6020-3:2015 establishes metric mounting dimensions for single rod compact series hydraulic cylinders with bores from 250 mm to 500 mm for use at 16 MPa (160 bar[1]), as required for interchangeability of commonly used hydraulic cylinders.
NOTE 1 This part of ISO 6020 allows manufacturers of hydraulic equipment flexibility in the design of metric cylinders and does not restrict technical development, but does provide basic guidelines.
NOTE 2 The compact series dimensions are most applicable to square-head cylinders.
ISO 6020-3:2015 applies only to the dimensions of manufactured products. It does not apply to their functional characteristics.

[1] 1 bar = 0,1 MPa = 105 Pa, 1 MPa = 1 N/mm2.