Well, what I am talking about is in the side gears of the carrier, if you look at the internal splines of the carrier, part way in there, will be a groove cut out. Then if you look on the splines for the axles that will be a ring about 3/16 of an inch from then end. The ring expands into the groove, and that is what keeps the axle from sliding out, it isn't a complete lock, but it holds it there, so that when taking the axles out of the diff, you have to jerk on it, and it will pop out. Most aftermarket diffs have the grooves cut in them, they can be used in an IRS or a solid axle, but I am not sure if the factory ones from a solid axle would have them.