Great question, Brian!
The bushings that fit on the bolts for the shackle straps tend to wear out a bit faster than the ones that connect your leaf spring directly to a hanger which is why there are only 4 bushings in the Dexter Heavy Duty Suspension Upgrade Kit for Single Axle Trailers # K71-358-00.
If you wanted to get 2 additional of the bushings that come in this kit then the part # D014-077-00 is the exact same bushing so you just need to order 2 of them as well. view full answer...