Our finish mower, brush hog and snow blade all have the same caster, wheel, tire and lynch pin setup. All are interchangeable, so I have 4 spares for any implement that may lose a tire. /forums/images/graemlins/wink.gif
I lost one of the lynch pins and one of the spacers when one of them got caught on some brush. Didn't run over the assembly, though. /forums/images/graemlins/shocked.gif
I went to a local supplier of wheels and casters for indusrial applications and got some solid tires for one set of the wheels. I like them so much that I swap them between implements(I'm too cheap to buy another set /forums/images/graemlins/tongue.gif).
I may just bite the bullet and get a set of solids, dedicate them on the brush hog and slip in some bolts.