Swivel to A3 Tower Bolts

Scored a set of Roswell surf racks with the mag swivels for $150 off FB marketplace (albeit w/ Centurion logos) .

They didn't come with the required bolts to mount the swivels to my A3 tower, so I'm in search of hardware. My dealer won't sell me any of their sets and Roswell hasn't gotten back to me...

Does anyone have a set of bolts laying around that would be willing to measure length for me? I'm assuming stainless machine threaded bolts from the Depot would serve the purpose?

Thanks in advance!