I'll see if I can explain it better. The carrier is the large center part that the ring gear is bolted to. Inside the carrier each axle goes into a side gear. Between the side gears are whats called the spider gears. On a Tracker set up there are two spider gears and one pin that goes through the carrier, through the first spider than through a spacer. It then goes through the second spider gear and out into the carrier on the other side. On a four pin carrier like a Samurai, there are four spider gears. Two are held in place just like the Tracker, the other two are held inplace by a short pin that goes through the carrier, the spider, and ends in the spacer, butted up against the long pin. These are generally considered to be much tougher because of the increased amount of parts to distribute stresses through, and that is why most companies that make lockers want a set up with 4 spider gears. Depending on what locker you buy, it will be set up to mesh with the original sidegears or it will have it's own replacement parts that fit in instead of the sidegears. I've heard on Sammi's that since the axle tubes are thin if there is any amount of bend in the tubes a locker with it's own sidegears is more likely to dissengage under stress, while a locker that uses the stock sidegears can have problems if there is much wear on the sidegears. That's probably clear as mud, but I don't have any pictures I can paste in to explain it better. It also means that regardless of what ring and ping gears you are using the center section is the same.