UIM class GT30 racing propeller. Fits Tohatsu 30 4stroke engine.

About size(pitch and diameter) and cupping:

Pitch determines the max speed that this propeller can achieve.

Diameter varies blade area, therefore affects grip. Bigger diameter = more grip.

Cupping varies from 1-6, where 1 is very "slippery" and 6 has very good grip.

The recommended sizes are preselected for your convenience. Preselected is choice for Tohatsu type C engine, 4 blade. If the propeller is to be used for UIM racing then preselected variant can be good average choice.