According to my Rohn catalog the bolts are as follows: 1/4 X 1 1/2" NF grade 5 5/16 X 1 1/2" NF grade 5 I used stainless on my tower but could not find NF bolts locally. I used NC with nylon locknuts. It's been up many years now with no problems. 73, Roger BTW NF = national fine NC = national coarse ( 1/4-20 and 5/16-18)