Had a similar problem just last weekend as had a puncture and locking nut had got slightly chewed so the special socket kept slipping off.
Pair of grazed knuckles later, made a trip to Halfords with the special socket and found a multi-faced socket (not normal hex) 2mm smaller than a normal nut £3-4. Hit it on with the patented "pursuader" i.e. a BIG hammer
then attached the long armed wheel brace. Bob's you uncle
Suppose it depends on what nuts (oo-er
) you've got on it. Mine uses an adaptor socket to fit into the normal (19mm) socket on the wheel brace so had enough room to put a normal socket on. If its actually a key you are missing then probably going to be a job to get off without the room to put a socket on. Hope you sort it