I agree with oldfoggie, I had an old Actuator that I reconditioned and everything was okay but that Bolt was frozen in rust. I carefully knocked it out and replaced with a Bolt from another Actuator that I picked up from a guy that was scrapping his Dish and Actuator, you need to regrease it, - I used white lithium greace.
I've had "regular"bolts snap on my 10' fiberglass dish, we get high winds here...Why in the world tell the OP he needs a grade 8 bolt? IMO nonsense. Any bolt that will fit will work. If you live where there's salt air of humidity, either use a stainless bolt or put some anti-seize on the threads/shank when you install it. You will destroy the dish and mount before you break a regular mild steel 1/2 inch bolt.
I've had "regular"bolts snap on my 10' fiberglass dish, we get high winds here...