This 8mm REX Bore Clamping Collar has a profile-matched bore in order to maximize holding force on the 8mm REX Shaft.  The 11mm diameter, 0.5mm protrusion on one side of the collar negates the need for a shim or shaft spacer between the collar and a bearing.  The protrusion will rest against the inner-race of the bearing, creating a little necessary space between the collar and the outer-race.  The M4 pinch bolt uses the same tool as you’ll use with 2800 Series Socket Head Screws that we use throughout the build system.