Sometimes referred to as a propeller (which it's not), the 1 inch | 25 mm diameter Kestrel Replacement Impeller with precision axle and low-friction Zytel® bearings fits all Kestrel models. Kestrel impellers are easily replaceable with just a push of a thumb. They will push right out and snap back into place. Our Kestrel Impeller's are tested twice for accuracy before they ship in a NIST certified wind tunnel.