Look at the 3rd item on the page. I tend to believe the postal weight, which says those dumbbells are 18.4kg, only 92% of the weight they're supposed to be, which seems like a bit much, even if I account for sloppy tolerances.
That leaves me thinking that dumbbells may have vanity sizing like pants do.
That leaves me thinking that dumbbells may have vanity sizing like pants do.