A very similar fitting to DIN, originating from Scandinavia and increasingly being specified in the UK.
Compatible with imperial sized tube 1″ od to 4″ od, The nut in Tp 304 is round and slotted, the male part and liner is Tp 316. The ‘square’ or ‘L’ section joint ring seal is EPDM. ‘C’ spanners are used to tighted the union.
BDE stock a range of hinged and pressed ‘C’ spanners to suit.