I have a question that's bugging me. It's not really important but I'm just curious. I put new rear Bilstein shocks on my 03 Trailblazer today. Since I was there I also replaced the rubber coil spring insulators on the top ends of the springs since they were getting old and crushed. Very easy job all around. Anyway, when I got the springs removed, I noticed that the left and right springs were different part numbers. One side is 15174231 while other side is 1517432. Both come up as coil spring part numbers online ( have been superceded though). I looked at both springs side by side and can see no difference. Why are there different numbers for left and right? I can tell you that the coil springs were replaced when the vehicle was fairly new. I took it in to the dealer because at certain engine speeds and conditions (like going up a small hill at 55 mph) there was a VERY loud resonance in the passenger compartment. There was a TSB about this problem caused by vibrations from the engine passing through the drivetrain up through the springs into the body. The remedy was to install redesigned coil springs. Afer they were replaced, this didn't happen any more. Anyway, back to the present...I reinstalled both springs on their original sides with the new insulators and everything went well. Just can't figure out what the difference is. Anyone know? Like I said, not important, just a curiosity. Looks like most aftermarket springs are just two of the same part number.