Just did a ton of power steering stuff, and 3/8" or 10mm works fine (on my '99 - I do not know if it changed over the years). The 3/8" I got was quite tight on the reservoir fitting, so the 10mm is more comfortable if you can find it. With the 3/8" (ID), be sure to lube it up so you do not break the fitting off. It happens a lot. :looney: Same goes if you are removing an old hose. Split the hose to take it off if it does not easily twist off.