pic: Question to the conveyor experts out there
 

Re: pic: Question to the conveyor experts out there
 

I don't see how those could keep a chain from coming off if it loosened... the chain will move away from those shoulders, not towards them, so the shoulders can't do anything to stop the chain.

I would venture a guess that you're seeing either sprocket clutches designed to prevent overloading, or quick-change sprocket hubs designed to allow easy servicing and replacement of sprockets.

Edit: http://www.mcmaster.com/#drive-clutches/=u9ywqt

http://images1.mcmaster.com/Contents...ng?ver=4353711

Re: pic: Question to the conveyor experts out there
 

Chains running off indicate an alignment or frame stiffness issue. In an industrial environment you are generally better off fixing the underlying issues than treating the symptoms. So mostly what James said.