Why do some flywheels take an allen wrench to get off and others bolts?

Question

Why do some flywheels take an allen wrench to get off and others bolts?

Answer 1

  Allen wrench, you must be working on a German car. You end up having to use an air hammer to get those things loose sometimes. I know that there are some that use the allen head for clearance, I cant remember what model of BMW I did that I noticed the small heads were the only way to fit. I have read that the allen head bolts have a higher breakpoint that standard head bolts too, maybe thats why?...  

Answer 2

Why not?

Answer 3

because the manufacturer wants you to either buy more tools or spend money taking it to dealer. must be a diesel.