This prop adapter is for a motor with a 2mm shaft and can accommodate a range of props with different size bores. GWS props with a 4mm bore fit on the 2nd collet while larger GWS props with a 3mm bore and hex head recess fit directly on the 2.9mm thread. Utilizing a grub screw to hold the adapter to the motor shaft makes this prop saver very easy to attach and remove and you don’t have to worry about stretching rubber bands and balancing as you do with other prop savers.