First off, is this an N/A or a SRT6 ?
If it's an N/A, then it is an odd tensioner by having the middle groove in the idler pulley, and no boss.
If it is an SRT6, then the ider on them has no boss. ( guess you could say it's independant, huh ? )
On the SRT6, you use the bolt to relieve the tension, I believe ( the service manual is not very clear on this )