This bolt is attached to the belt tensioner / idler pulley on the lower side of the motor on your 2003-2006 Nissan 350Z / Infiniti G35 equipped with a VQ35DE powertrain. Improper adjustment and rust cause this bolt to seize or bend making it difficult or impossible to to achieve proper belt tension. This can be purchased as a bolt-on assembly if necessary HERE.
There are two separate belt tensioners on your VQ35DE. This listing is for the accessory belt tensioner bolt for the accessory (alternator) belt. A/C Belt Tensioner Bolts can be found HERE.