Here in New Zealand, 37-38-39 skirts all look the same, except that 37 skirts are about an inch bigger in circumference, and are too big to fit the 38-39 wheel arch. When you try to put a 38-39 skirt on a 37, just about falls right thru. 37 skirts will fit 36's perfectly....must be same wheel arch. Due to ww2, we never got any 40's here.