I've seen too many one wheel missing landings to be enthusiastic about wheel collars. I always solder washers on both sides of the wheels. Been doing this for years and have never lost a wheel due to the wheel collar falling off. One way is to cut the axle the width of the wheel plus the thickness of the washer + 1/64". Then punch a hole in 1/64" plywood or a calling card. Slip it on the axle between the washer and the wheel and solder the washer in place. Remove the 1/64" spacer and you have a free rolling wheel with a smooth finish on the washer which is very unobtrusive.