The sizes vary.
A Vernier caliper, soft tape measure (and some math) or a crescent wrench (tightened around the bar and then use a tape to measure the gap between the jaws) are the only ways to know for sure.
yeah spend the money on a caliper. By the time you buy 3 sets of bushings that are the wrong size you'd have the tool paid for and can use it for other things. Been there done that