Think of pitch in the same way you think of threads on a screw.
A pitch of 6 means in one revolution, a propeller should move forward 6 inches.
Generally, greater pitch yields faster cruising speeds; lesser pitch provides better climbing.
Starting Propellor sizes are mid range pitch props that should fly just about any plane designed for that size engine.
Use these first as in most cases they will be close to being the correct size.
Then use trial and error to try and fine tune the maximum performance from your ship by trying the alternate props.
If none work better stick with the recommended starting prop.

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