Screws or rivets hardware to boom?

[Jim Cate]

Monel is I believe a type of steel

Nope, Monel alloys (and there are many such) are cupro-nickel, no iron involved, and such are not a form of steel.

Good stuff, that!

Jim

[RaymondR]

One of the advantages of rivets is the self centering effect when you need to drill them out.

[SaltyMetals]

I user the 6 (or is it 6.4mm?) rivets and the Al rivets are ok with the usual pop rivet hand tool. Just impossible on the monel rivets which are much stronger so i borrow an electric tool from the riggers if using monel.

[blueazimuth]

We've had similar questions here before and the answer is the always the same - use rivets, not threaded s/s screws.
Tapped s/s screws will cause corrosion, even if Tuf-gel is used and, when corroded, will almost always snap off when removal is attempted, and are a real bear to drill out.
In any case, the wall thickness of masts and booms is too thin to support the engineered number of threads.
Look at the other fastenings on your mast or boom and duplicate what the professional builder used. The correct rivet has high sheer strength except when mounting winches when Rivet-nuts are recommended.