What size is this nut?!

[Peg8687]

The nuts that bolt the H-Pipe to the Headers (FRPP "P" headers)...I Guess one of mine came loose...Bc i could not find this exhuast leak. I changed header gaskets 100x but never fixed it. Crawled under the car and low and behold missing a nut...Anyone know what size this is so i can go get a new one ASAP

 

[needforspeed440]

not real sure had the same problem though, my stud fell out though so i had replaced more than the nut. I would take it one off the other side and take it to the hardware store and try a few bolts.