We have used this molded 5/8" x 3/4" Heater Hose many times when plumbing into a modern LS or LT engine. The stock GM LS & LT engines have pressed-in barbs in the water pump. The smaller 5/8" barb is the pressure port and the larger 3/4" barb is the return port. Both of these barbs point directly toward the passenger side front wheel. This molded 5/8" x 3/4" hose works great with the big end on the water pump's 3/4" return barb with the 5/8" end connecting to the heater core fittings. Use this hose in conjunction with #31800-VUD 5/8" bulk hose on the water pump's pressure port. This molded hose is sized at 5/8" for the majority of its length with a 3/4" bell molded into one end. Overall hose length is approximately 60".