Product review (5 stars): These fit perfectly and even if the holes don't line up you can make them work if you're handy with a drill!
For those wanting measurements for the mounting holes, here are the measurements from the manufacturer and I even took the time to verify the measurements against my set:
A.  The two outer holes for the fan blade measure 3 - 15/16" apart on center.
B.  The distance from either outer hole to the single center hole is 2 -5/8".
C.  The two holes to mount the arm to the motor measure 2 -1/16" apart on center. (Measured from the center of both holes)
I've provided a customer image to help explain.

I doubled checked these with my fan blade arms and the measurements check out.  I hope that helps someone out!  Just don't get mad at me if the manufacturer changes things up at some point.

I just used a set of these to save an aging ceiling fan in my parents' house.  I was helping my momd dust an old ceiling fan and I just lightly touched one of the blades and it fell off. It must have been cracked and waiting to let go. I'm just glad I found it this way instead of turning on the ceiling fan and discovering it the hard way.

These blades fit perfectly on an old fan that isn't even a Westinghouse brand. The only measurement I was concerned with was the width of the bracket going to the motor.  The holes lined up just fine but the bracket width of the motor mount area itself was a little larger. Fortunately it wasn't significant enough to cause any fit issues. (I was worried about possibly needing to grind down the ends of the mounts at first glance.)  These feel a little lighter than the originals but they still feel sturdy and well made.

PROS:
+  Affordable and much cheaper than replacing an entire fan (This saved my parents $100 )
+  Easy to install if the holes line up
+  Hardware to mount the blade to the arm is provided.  (You need to reuse the old screws that mount the blade arms to the fan motor itself)
+  A set of 5 maintains balance so you don't get a wobble or off balance fan from using a mix of old and new arms.
+  Even if the holes don't line up correctly for the fan blades you can drill new holes (Just make sure you follow the instructions and keep things centered.)

CONS;
-  If the holes don't line up you may need to drill your fan blades
-  I understand why but you can't buy these unless you buy an entire pack of 4 or 5.  If you'd break a replacement mount again in the future you'll still need to purchase 4 or 5 because that's how they're sold.

TIPS:
-  You really should replace ALL of your old fan blade arms even if only one or two are damaged. This is recommended to maintain proper balance.  These replacements almost definitely have a different weight than the original  fan blade arms. Having a lighter arm on one side and a heaver arm on the other can lead to balance problems, wobble and more. Play it safe and take the extra time to replace them all.

-  Save your old/existing screws that mount your fan blades to the fan itself. (2 per fan blade arm) These screws aren't provided with your purchase and you'll need them to reinstall the fan blades.

-  The most important/critical measurement is going to be the measurement for C. (the distance between the two holes that mount the fan blade arm assembly to the fan motor itself.  You can always do a little drilling on the fan blades themselves if the other 3 holes don't line up properly.