They are Dubro wheels:
http://www3.towerhobbies.com/cgi-bin...&I=LXD787&P=SM
They are secured with a cotter pin pushed through a drilled hole in a piece of brass tubing. The brass tubing is cut longer then the landing gear axle leg and soldered to it. I use a washer up against the outside of the wheel and install the cotter pin through the drilled hole.
Bob