the RANS riser is already slotted and drilled and is larger than / fits over the existing 1 1/8 steerer. A compression/pinch clamp will go around all of that, and snugs the riser onto the steerer just like any other threadless stem. I can still stack it higher with spacers, but don't really need much - the steerer goes up almost to where the bend begins, which I hope makes for an even sturdier connection.