nuts and bolts question

Would some one please tell me what the Spec.s are for the bolt that holds the oil pan to the engine block. 1987 SR-5, 2wd, 22re motor. My predicessor lost an original bolt (from the pan) and has installed a (what looks like) a 5/16 dia. SAE bolt into the hole, i have inherited a oil leak. I have only examined this installation, and would like to gather some Taps and Bolts before indulging on this venture of replacement. Thanks for your help, i'll just stand back and read!

UPDATE!! 1st i want to thank you for looking and your regards!
I recently purchased the lil trk and i knew it had some issues. I made a priority list & began to check them off..have eliminated a few. One of the Prob's is a persistant oil leak from a bolt, that was installed in the oil pan at an earlier time.

The bolt in ?, holds the oil pan to the engine block and is located left of center, under the Crank.

Being more familiar w/chvys and frds, i assumed that the bolt will be the same lenght&deminsion as the bolts located on the sides of the pan!!! BUT, after reading several threads, dating bak to 94, i have re-directed my thinking and question?. Could this bolt, hold the oil pan as well as some internal part?, of which i am unable to see??????? could this bolt have a critical design strength built into it????

I have not removed the bolt in ???? or any other bolt on the pan for fear of creating some irreversable prob., that i may not be prepared to address at the time.

I have researched some of the web sites which show diag.'s of timing chain install. Perhaps someone may know of a web page showing a exploded view and or a detail diagram refering, to this area of the 22re motor, front of oil pan,bolts,gaskets and internal components ect??? Thank You again for your time and consideration.