It's 45mm (1 3/4") in diameter and has a metal backplate with socket head machine screws to hold the cone on. It's a nice unit that I've been flying for a couple months now. The adapter ring that is the closest to the shaft for the Spektrum Avian EF-1 motor needs to have the ID reamed a bit for a perfect fit. This type of spinner would also allow someone to drill out/open up the tip of the spinner for cooling flow to the motor.
One of the best things about it is, this is a nice quality spinner for only $7.64?
Here's a link to it on their website: https://gator-rc.com/gator-lite-spinner ... late-white