This Prop-Saver Adapter is the same one that is included with 2205, 2208 and 2212 series Scorpion Brushless motors. Machined from High-Quality Aluminum bar stock, it is designed to fit on a 3mm motor shaft, and comes packaged with 2 replacement rubber O-rings. One side of the adapter has a tapered boss with a maximum diameter of 6mm and the other side has a tapered boss with a maximum diameter of 5.5mm. The Scorpion Prop-Saver Adapter weighs 2.0 grams by itself, and 2.4 grams with one of the O-rings installed. It can be used on any brushless motor with a 3mm shaft, and is recommended for use on motors of 200 watts or less.