I bought a big bolt with a 3/4" head on it and then threw a nut on it and welded the nut to the bolt. Throw the socket wrench on that and done. Couple bucks.
I had the same issue last week... Drove to harbor fright no go a, then on way back home saw a flea market going on, paid my .75 cents to get in and found one for two bucks... It was a L shape Allen so I used the bar off a tube bender to loosen it up....
I believe its a 19mm allen key. ordered one off of ebay cant remember but not much plus I needed it. Suggest getting two of them in case the axle starts rotating. Used a piece of pipe as a cheat bar. Front wheel is 17mm.