1503 Series M4 x 0.7mm Shoulder-Standoff (5-6mm OD, 10-19mm Length) - 4 Pack

These shoulder standoffs allow you to mount 3600 Series V-Wheels, holding the center of the wheels 24mm off the surface the standoffs are fastened to.  Keeping the center height, and therefore the center of the goRAIL, on a standard 24mm spacing keeps your project on pattern.