I'm changing out my chain and sprockets to a 520 conversion but I'm not sure which way the front sprocket faces. How can I measure which way it faces with one side having a shoulder and not the other?...

When I got to taking the rear wheel off, trying to loosen the nut did not loosen the nut. Checking the other side of the axle confirmed that it's just spinning the axle as a whole. It even started rot...