Can I use the top and bottom boxes separately or do they have to stay together?

The units are designed to lock together for transport but separate easily when you're working. Use them independently at different workstations or stack them when you need to move everything at once.

What size tools and parts fit in each compartment?

The compartment dimensions aren't specified in the product data — measure your largest tools and fastener containers before ordering, then test-fit when it arrives to confirm they work for your setup.

Do the wheels lock or just roll freely?

The locking mechanism isn't detailed in the product specs. When your trolley arrives, check whether the wheels have built-in brakes or if you'll need to chock them during work.