hi fellas. first post, could use some help. Bought a replacement serpentine belt for my dads rav4. Not sure exactly which nut to use to loosen the tension. I see a small round pully with an odd shaped hex nut, seems to require a special tool cause its somewhere in between 13 and 14 mm. Also, see some other larger hex bolts nearby. Not sure exactly which one is the tensioner adjustment.

Found two threads online. One mentions that the small center pully requires a specialty tool. The other threads I saw indicated that the tensioner was not adjusted from that central, small pully.

thanks for any help you may have.