This part of ISO 9803 specifies mounting dimensions for vacuum pipeline fittings (elbows, tees and crosses) of non-bakable and non knife-edge flange for nominal bores from 10 mm to 250 mm of the R5 series.
BS ISO 9803-1:2007 history
2020BS ISO 9803-1:2020 Vacuum technology. Mounting dimensions of pipeline fittings. Non knife-edge flange type
2007BS ISO 9803-1:2007 Vacuum technology - Mounting dimensions of pipeline fittings - Non knife-edge flange type