You're talking about the knurled knob that sits just above the filister screw right? i have a V2 but don't have a caliper to give you a scientific measurement, but with my trusty and fairly accurate ruler, i measure it at 1 3/16 cm in diameter and 1 cm tall from base to tip with .5 cm being the knurled edge, and the other .5 cm being the smooth cone tip. hope this helps. keep in mind that mine is fan made and not MR although rest assured that the maker went to great lengths to ensure accuracy.