Yeah I know, big newsflash, right? Well, What I'm talking about is you might find minor size differences between props from different manufacturers that are supposedly the same size. I discovered this when I decided to buy a new set of 13" props for my Tarot FY680 Pro hexcopter. I had removed the props I had on it and put four of them on my Elev-8 quadcopter (I had modified it and it has the same motors as my Tarot ship).
When flying the hexcopter with its new propellers, I noticed an odd sound - like the prop tips hitting something. Fearful that there might be defect or something worse, I landed it and examined everything. I couldn't find anything wrong - no signs of cracks or defects - all screws were firmly in place. But on subsequent flights the noise persisted. Upon a re-examination, I noticed that some of the adjacent prop tips only had a about an eighth of an inch of clearance; some flex in the booms while in flight might cause the tips to come in contact...
After comparing the length of the one of the new props to one of the old ones, I discovered close to a quarter inch of difference - the new propellers are a tad longer and wider than the older props. The length difference is just enough to cause blade tip contact between adjacent props on a hex or oct copter.
The new pro is on the left. The pitch is the same on both props.I have decided to put the old props back on the Tarot machine and I'll use the newer ones on the quad, which has much more clearnace.
The other thing I've noticed is different performance. With the issue I've had with my mini build, I did some tests. One thing I found is that HQ 5040 tri props pull about 3 amps more at 75% throttle than identical 5040 X 3 Genfams
Well, I think I discovered that the problem I experienced was not due to prop length, though that it something you should be aware of... I suspect that the problem was due to my not putting the little caps on three of the props - there's a little "cap" that goes over the center of the prop and then there are two screws that hold the whole thing together. Not having the cap on, I suspect, allows the prop to move slightly up/down the spindle.
At any rate, I've put the slightly longer props on the quad and the slightly shorter ones on the hex and both aircraft fly fine.