Take a socket set and test each socket until you find the correct size that fits snugly.
The shorter bolts go on the outside corners.
The bell housing bolts are 3/8-16.
It's on the transmission, two 14mm bolts.
13mmbolts. gmjim
9`16
It uses a 46RE transmission.
10mm or 12mm metric 10mm or 12mm metric
there are three sizes 3.5" 6.5" and 6" by 9"
1 17mm in front and 2 14mms in back.
Try a wrench on them and find out what size they are.
what size wrench is used for tranmission plug on a 2001 Avalon
most likely a 10mm or a 3/8"