Is 3/4" on one end. Should have known -- Autozone convinced I have a 3/4" heater hose in there somewhere. Loves to sell me valves and heater cores with one 5/8" nipple and one 3/4". Trust me: have five of the things covering all 3 years of production -- no 3/4" heater hoses. Went back to tower valve I usually use (including DeLo). Factory Air #74612. Good news is only costs $10. Bill Robertson #5939