My NDZ rail had screwed up, so i needed a new drop. I saw that this had 3 holes to lock it down, so i got it. It's a really neat design...when i got it i wondered how the heck it worked, but then once i looked at it for a second i figured it out.It has three screws going through it, and the rail on the bottom. You slide the rail on, and then tighten the screws.They push on the other side of the rail, and it makes it wider.It does a great job of holding it on, and its made by CCM.
Get this over a regular rail with a ball bearing...it'll hold a lot tighter and last longer.