This unit has a blind hole for the motor shaft. The front of the adapter becomes the front of the shaft. A 1.4mm nub centers your prop. Made for props designed to press onto 1.5mm shafts. Perfect to get your GWS 3-2 or 3-3 prop mounted with a saver on your brushless motor. We suggest our small o-rings above for use with this saver. The included rubber bands are of poor quality and should be discarded. SKU Number: RRCPS15NUB