If you start from scratch, sure.

But if you're e.g. repairing existing equipment, then the customary and SI units are incompatible. Say, a 1/4 inch bolt head is too large for a 6 mm wrench, but too small for a 8 mm (which is typically the next step up from 6mm).

For this reason I had to buy some wrenches in customary units to fix a lawnmower engine.