Ab iron

May be a dumb question especially because I do not plan in ever making an ab iron. But what does it mean when it says radius of no less than 18 in.  U thought u understood radius=1/2 the distance of the circumference. There got it doesn't make much sense to me.

Thank you
Robert.

if you draw a circle with a 18" radius the ab iron cannot  have more curve than that circle.

I see. Thanks