I recently swapped out my UL 350iS for a Rotax 912 ULS because of the way UL attaches the prop flange to the end of the crankshaft. Instead of forging the flange as an intregal part of the crankshaft, UL has a short (less than 1/2") spline on the end of the crankshaft that engages a spline on the prop flange which is held in place with a large ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.