Be sure to apply grease to the ring and pinion gears. The trucks ship dry which is beyond me. Check the transmission also, there's no grease in that either. Kinda stupid if you ask me.
It was a pair for $10. They come in a few colors. The holes are not threaded. The single top center hole is and it came with 2 screws but I'm not sure what its used for.That's awesome! I'm glad I was wrong. I found someone's link that said they were about 3/4" too wide, very cool though. Are these sold in pairs or individually?