Pitman arm and idler arm bolt size?

[1sttimeexpo]

All right so I decided to change out my Pitman arm and my idler arm simply because I just want to do something with my truck in my suspension is already kind of new. My question is the Pitman arm has a size difference of 2 1/2 and 3 1/2 so which size do I need? Or if nobody wants to say tell me how to figure it out myself other than Google

 

[riphip]

First: what year, trim, etc, etc? Not much info to go by here.
Second: Do you own a tape measure, ruler, etc?
You can measure the size on the truck now to determine your need & match it.