This part of ISO 3601 specifies the housing (gland) dimensions for class A O-rings for general industrial applications conforming to ISO 3601-1, as well as housing dimensions for class B O-rings used on selected metric-dimensioned hardware, e.g. fluid power cylinder bores and piston rods. These O-rings are for use in general hydraulic and pneumatic applications without and with anti-extrusion rings (back-up rings). The dimensions of the O-rings (d1 and d2), size codes (SC) and tolerances conform to ISO 3601-1. Housing dimensions for the O-rings intended for aerospace applications that are specified in ISO 3601-1 are addressed in informative Annex A. NOTE 1 It is expected that O-ring housing dimensions for special applications be agreed upon between the O-ring manufacturer and the user. NOTE 2 The terms “housing”, “groove” and “gland” are interchangeable, and their usage is a matter of local convenience. In this part of ISO 3601, the term “housing” is used exclusively.