Used on 2320-01-465-2174 mk23, 2320-01-465-2176 mk25, 2320-001-465-2180 mk27, 2320-01-465-2182 mk28, 2320-01-465-2186 mk29, 2320-01-465-2189 mk30, 2320-01-530-5693 mk31, 2320-01-465-2260 mk36, 2320-01-504-5218 mk37, part of armor kit. o-ring one oring is placed on the bump-tube of the fitting at the hose end no 1