This Scorpion SII-4020 & 4025 Bolt-on Prop Adapter is the same one that is included with SII-4020 & SII-4025 series Scorpion Brushless motors.

Machined from High-Quality Aluminum bar stock, it is has a 8mm threaded prop shaft.
The Scorpion SII-4020 & 4025 Bolt-on Prop Adapter weights 40 grams.

Specifications :

Thread size M8*1.0