Yes, it's true that almost all propellers are stamped in some way to designate diameter, pitch, and rotation.  For inboard props these stampings are generally found on the side and/or end of the hub, and will look like this:  24 RH 26.  This designates a propeller that is 24" in diameter (the diameter always comes first) by 26 inches in pitch with a Right Hand Rotation.  Some I/O or outboard props are stamped for diameter and pitch, but many only carry a part number which must be cross-referenced to a manufacturer listing to determine the design dimensions.

So, "I can determine the size of my propeller just by looking at the stampings".  Sorry, even on brand new propellers we've found the pitch to be off by up to 1" overall and up to 1" between blades from the markings, so your propeller may not have ever been the diameter and pitch it was marked.  The only stamping that's likely to be accurate is the rotation.  To complicate matters even further consider the following questions:

Has my propeller ever been reconditioned?  If it was done on pitch blocks, how accurate (generally not very) were they?   In the finishing process did I lose diameter when nicks and dents were ground out?

Has my propeller ever been re-pitched or had the diameter changed?  If so, was it done accurately?  Was the new size re-stamped on the prop or does it still carry its' original markings?

Is my propeller cupped?  If so, what size cup (we use twelve levels of cup)?  And is the cup even on each blade?

It's easy to see why the stampings on your prop may not accurately reflect its' true size, and this can be a real "knock out punch" when you're trying to improve performance or get to target rpm's for your engine.....You just can't get to where you want to be if you don't know where you're starting!

For these reasons we offer a NO CHARGE computer analysis for your inboard propeller in our shop.  We'll measure it on our computer system and provide you with a detailed size and condition report.

Back to FAQ's