First, I attached a 25 pound weight (get the ones at WallMart, about
$10 for a 25 pound weight) to
the rear wheels of the tractor. These weights fit right into the taper
in the tractor wheel.
Drill and tap holes to match the ones in the tractor wheel. I
just used two, as the weight wedges into the
taper in the wheel and is held securely in place with just two bolts.
7/16 x 14 was right for my tractor,
but you'll want to check yours. I don't know if they are standardized.