how can you distinguish a factory labbed merc. prop from a non labbed prop?

Well there are several things to look for but thinner blades with sharper edges and a satin finish.

Julie

Look at the aft side of the prop hub under the nut. If there is a hand stamped group of letters and or numbers, it may be a Merc worked propeller. The letters and numbers are coded to tell small amounts of information. This doesn't tell if it was reworked by anyone else though. It just tells Mercury Racing has worked on it at one time. A trained set of eyes can tell if it is still a Merc Lab. If you need help determining more, give us a call with the code.