Rubber push-on hose with a 3/8 inch, 9.52mm internal bore. This is the workhorse size in a push-lock system, covering fuel feed and return, small oil lines, coolant runs and breathers on the majority of builds. It is designed around push-on barbed hose ends: push the hose fully over the barb and the profile holds it without clamps, crimping or special tools, which makes a system quick to plumb and just as quick to modify later. Use assembly lube to ease the hose on. It suits push-on fittings only, not PTFE or stainless braided ends, and a clamp remains sensible on pressurised lines.