Do I need to remove the pipe to use this expander?

Depends on your setup. If you're flaring or swaging a line that's still in the engine bay, access matters more than the tool itself. Test-fit the kit handles in your work area first — these are hand-operated, so you need room to work the lever smoothly without obstruction.

Will this work on stainless steel or just mild steel tubing?

The kit is designed for standard tubing materials used in automotive brake, fuel, and coolant systems. Stainless is harder and will require more hand pressure; start with lighter force to feel how the tool responds before committing full leverage.

What if I need to expand a size between the marked diameters?

The expander heads are sized for the five diameters listed. If your pipe falls between those sizes, you'll need to test the closest head — some overlap is built in, but forcing a mismatched size can damage the tool or crimp the tube. Contact support if you're unsure about your tube diameter.