Helps one decide the appropriate size of hole to which an LED may be placed comfortably and an exact fit without undue stresses on the holder.Supports min 4.7mm to 5.8mm max diameter in steps of 0.1mm.The thin 1mm height helps not to interfere with the luminous spread especially in wide beam angle LED's i.e:Strawhat LED's.Useful in locations where you may not have a reliable measuring tool at hand.For the STL file check http://www.thingiverse.com/thing:378764/