This is a APC 8x4 Thin Electric Composite Propeller .

Diameter: 8"
Pitch: 4

For use on Electric powered aircraft only (not for glow engines).
This is a prop aiming for high speed, not for general flying
Gray composite propeller blades that assemble onto a propeller hub.
Comes with five adapter rings that adapt to different motor shafts

Adapter Rings 3.2mm (.128), 4mm (.158), 5mm (.197), 6mm (.237) & 8mm (.313)

This Propeller is for Electric use only.