RE: RC Surfer
Jimi,
If the coupling is the wrong size for the motor just contact the seller as ask of you can swap it if you pay for postage, or just keep it as one day you will have a motor with a 5mm shaft.
If you bought your motor from John then he maybe selling gear that has imperial sizes not metric, check it out and buy accordingly. If it has a 1/8 motor shaft buy a 1/8 coupler, don't buy a 4mm as you want a perfect fit!
Shame about all the set backs, you'll get it up and running soon and it will be worth it.