Service Instruction: Installation of a propeller by usage of round-neck nut set for ROTAX® 912, 914, and 912 i (Series) Aircraft Engines

The advantage of the Rotax inserts is the fact they are fully tight into the flange, no side clearance.  The thread to this type will have less clearance to the bolt than the bolt passing into the flange with no insert and a washer nut on the inside.  The idea of drive lugs is better to hold the torque load compared to just the bolt itself.  

Cheers

That makes sense RW.  My prop does have drive lugs, but they are hand inserted and not as tight in the bore as the Rotax inserts.  

I see most people still use lock-nut type nuts on the back of these flange inserts.

Roger,

Are you saying that most people use the Rotax “Threaded” insert with a lock nut behind it as extra security, or do you mean most people use a non-threaded insert with the lock nut as the only securing means?