Most likely thery're 3/8-16, grade 8, around 3/4" or 1" long. Places like Tractor Supply or Fastenal should have them on the shelf. You could also use Allen socket head bolts- - - -all the above are available by the thousands on Ebay. "This ain't rocket surgery!"
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!