2nd Gen Non-Engine/Transmission idler arm question

[CEdwards]

Just ordered a new idler arm from NAPA today. It called for 3 different sizes. They said to measure the diameter of the bolt in the frame. It measured 12. 5mm so thats what I ordered. After researching it on here someone posted all 2x4 3/4 tons use 16. 5 mm. Does anyone out there know? Did I measure the right thing? I need to figure it out so my trucks not down all week since napa is closed on the weekend and it will have to be ordered. By the way the cost was $60 at napa, it was also posted over $200 at dealer. Does this price sound right? thanks.