Boxter 99: What bolt is this?

[hoemanna]

Hello there,
Today I heard a short squeaking and believe I am are hearing a faint rattling under the vehicle now . I have found a bolt (rough dimensions only) diameter 17mm (2/3in) , internal thread M10 through hole, length without head 20mm (4/5in) and wrench size 24mm (about 1 inch, see photos ) . The bolt was very hot . Can anyone tell me what this is ?

[BYprodriver]

That secures the belt tensioning roller. Remove the engine access panel behind the seats.
Don't start the engine until it is properly secured. Good time to replace the belt. That "bolt" is very difficult to properly torque with engine in car. Previous installer obviously failed!