I have seen this too and all our Lego is legit. In fact, I was picking some for an order a few days ago - 3 sizes - and automatically looked at the ends for the size number. In this case, there were no numbers and I figured I had been mistaken in thinking they were there. I'm now going to check my inventory.
Also see this: https://www.lego.com/en-SG/service/help-topics/bricks-and-sets/themes/technic/measurements Possible useful PDF.
Update: I now know where I've seen the number. It's on the various connectors - not the axles. I had considered it was on older versions but I was wrong. The pdf is good to have. Have just printed it and will keep it on my work bench.
Comments
In fact, I was picking some for an order a few days ago - 3 sizes - and automatically looked at the ends for the size number. In this case, there were no numbers and I figured I had been mistaken in thinking they were there.
I'm now going to check my inventory.
Also see this: https://www.lego.com/en-SG/service/help-topics/bricks-and-sets/themes/technic/measurements
Possible useful PDF.
I now know where I've seen the number.
It's on the various connectors - not the axles.
I had considered it was on older versions but I was wrong.
The pdf is good to have. Have just printed it and will keep it on my work bench.