Distance Collar

Recently, a list member working on his ST1100 rear wheel for the first time posed a question. "I can't get the rear wheel back on the bike," said Len Freedman. "There's too little space for the rear brake caliper support bracket to fit. The gap is about an eighth of an inch too small. Help!" This had everyone stumped for a while. It turns out that the distance collar was not installed correctly.
What's the distance collar? The arrow points to it, the steel tube poking out from the final drive.
Notice that one end of this nicely cleaned part is ground to a smaller diameter than the other end. (You might not notice this if the part is smeared with a thick coat of moly paste, as Len's was.) The ground end must be inserted first into the final drive. There's a small witness mark (arrow) showing how much engagement the collar has with its mating part in the final drive assembly. The end of the collar visible in the first photo is not ground.
Len's problem was that he was trying to reassemble his bike with the wrong end of the distance collar facing out. I had no idea what his problem could be, because the distance collar had never come out of place whenever I had removed the rear wheel from my ST. The error he made shall henceforth be known as "A Len Freedman".