Hex bolt?
For instance, a 1/2" diameter bolt is almost the same size as a 13mm bolt. However, there are 25.4mm in an inch. 25.4 x .5 = 12.7mm. So, you see that a 1/2" bolt is actually a hair smaller than the 13mm. Meaning, if you got something that used a 1/2" bolt, but the bolt was not a tight fit, you can substitute a 13mm to make it fit.
Also, figure out what is supposed to pivot. If the bushing pivots around the bolt, don't do this. But, as with a rod end, the bushing pivots inside a race, you can try it. Heat up the bushing in your oven (don't burn it by overheating anything rubber or poly). Stick the bolt in the coldest part of your freezer (or grab some dry ice from Wal-Mart). the bolt will shrink and the bushing will expand. Stick the bolt in the bushing. When they return to room temperature, the bolt will expand and the bushing will contract. The resulting bond is almost like them being welded together!

