So i just got a hole in my upper rad hose. when i looked online to see my options for silicone hoses there are options for a 2 piece and a 3 piece hose set for upper and lower. i found a cheap set thats a 3 piece but im wondering what the small section is for? its for my s13 so rwd. anyone ever used these before? if this doesnt work out ill just order the 2 pc. i went for the cheap route just out of curiosity.

Small section is for the lower radiator hose. There is a fitting coming out of the block, then it goes to a tee of sorts that feeds coolant back into the block from the heater core, then the main radiator hose connects to that.