5. Two Acroname or Lynxmotion servo wheels. These wheels are 2 plastic wheels that are designed...

5. Two Acroname or Lynxmotion servo wheels. These wheels are 2 ¾ plastic wheels that are designed to attach to the servo’s output shaft spline. Prather Products 2¼-inch aluminum racing wheels with rubber O ring tires, Tower Hobbies #PRAQ1810 or Hayes Products #114, 2 ¼-inch hard plastic racing wheels (also available from Tower Hobbies)

can be used as a substitute. These somewhat smaller two alternative wheels will work, but they do not have the spline to match the servo output shaft and are a bit more difficult to connect reliably than the Acroname or Lynxmotion servo wheels.