Is it the wrong tool? I've searched and the same part number (915-0207) was recommended for the job I'm doing in another post.
http://www.peachparts.com/shopforum/showthread.php?t=179301&highlight=915-0207
The Baum Tool catalog (and the Fastlane special tool link) shows I have the right tool for rear axle bearing retainer nut removal. The ~0107 tool is listed for differential pinion retainer nut removal (which would be on the propeller shaft flange). I don't know why Baum Tools told me I needed that tool when I explained to them what I was doing. They even compared sizes of the two tools in hand over the phone and the 0107 tool had a much smaller diameter. I have a 1mm problem, so that doesn't sound right.
Do I need to remove anything from the bearing assembly before I use the groove nut socket? It didnt appear that way in the FSM.