[TowerTalk] To pin or not to pin

[Rudy Bakalov]

I am getting really tired of my mast slipping during major wind gusts. The mast is supporting a 4 el 40m M2 yagi and a 6 el M2 KT36XA. The clamp is the standard clamp that comes with the ProSisTel PS61D rotator.
So the question is if I should pin the mast to the rotator clamp using a M8 bolt. The clamp has 8 bolts, but clearly the friction between the clamp and the mast is not sufficient under extreme conditions. My one and only concern about pinning is that the hole in the mast may weaken the mast. The PST61D is rated for 36 sq.ft so, right or wrong, I am not concerned about the wind damaging the rotator.
If you suggest I pin the mast, there are two follow up questions:
1) What grade bolt should I use for the pin? The mast is 120K psi. Should the bolt be rated for less (e.g., Grade 5) or more (e.g., Grade 8 or 10.9) psi? That is, do I want the bolt to break before the mast does under extreme conditions?
2) Further, is it OK if the bolt is zinc plated? I could not find stainless steel Grade 8/10.9 M8 bolts. Is the contact between zinc and the mast going to lead to corrosion?
Rudy N2WQ