Like most Americans, I think, my mind thinks in Imperial simply from a lifetime of using it. I think in miles and pounds and gallons.
I can understand volume and length in Metric without too much trouble, but Metric weight is something I can't seem to grasp.
They say a paperclip weighs about a gram. So a kilogram weighs as much as a thousand paperclips? I have a hard time imagining how heavy or light that would be. And when you get into lots of kilograms, I'm just lost.
Metric tools are no problem at all.