When we bought Anne Marie in 2015 she was out of the water and very poor condition. Like everything else the masts and booms had seen better days however replacing them was out of the question financially so repair was the answer. The main boom was built for slab reefing where you reduce sail area when the wind rises by dropping the main and setting less sail area.
How slab reefing works: Reduce the amount of sail by bunching the bottom slab along the boom. You reef a sail in strong winds to make the boat sail better and safely.
Slab reefed sails have a set of eyes built in in two or three layers , one at the front by the mast (the luff) and the other at the rear (the leech). This sail is lowered down to the point where the first eye can be looped onto a hook at the front of the boom. The eye at the back of the sail has a rope through it which you haul outwards to fix the sail in its lower position. This rope goes from the sail to the back of the boom and is threaded inside the boom along its full length coming out at the front by the mast. Generally there are clamps at that point for tying the out-haul therefore fixing it in place.
You can see from the photos that the clamps on our boom were heavily corroded. So much so that they would not budge and the only thing to do was to drill them out and remove them. Try as I might I could not find any replacements so recently my family gave me three stainless steel cleats which I have fixed to the boom and these will enable me to haul on the ropes and tie them off.
Original system 
Original clamps with one removed 
I measured it just in case I could find a replacement.
Saving Anne Marie 