HOW TO MEASURE LIP AND BARREL SIZE
Below is an example of a wheel with reverse parts. The concept still applies with step wheels. Wheels that are sandwich mount you will also need to account for the width of the face inbetween the lip and barrel.
The photo shows an 11" wide wheel. Like all wheel manufacturers, the width is measured from bead to bead, not from end to end. The wheel below has a 5" outer lip and a 6" inner barrel. As you can see, you only measure up to where the tire beads up, not the overall width to the very end. You will need the tire off to measure properly like the photo.
This is the only correct way to measure to ensure you order the correct size parts you need.
HOW TO MEASURE BORE SIZE:
WHAT IS THE DIFFERENCE BETWEEN STEP LIP AND REVERSE LIP?
WHAT IS THE DIFFERENCE BETWEEN STEP BARREL AND REVERSE BARREL?