I'm not sure which bolt you're referring to. The outboard/end casting is just slid into the front crossbar and held in place by the tie rod. The tie rod passes through one casting, underneath the dolphin striker post (directly under the mast base) and then back through the other casting. The tie rod is threaded on the ends with fine threads, and a heavy SS nut is torqued onto the ends to put the tie rod under tension. This serves to reinforce the forward crossbar under the weight of the mast and the downward force of the rigging. If the tie rod has snapped, this is not good and should be replaced immediately before sailing, or the crossbar could break in half.
In addition to the tie rod, there are two bolts in the area of the end casting. One bolt is a through bolt that holds the very end of the casting down to the outboard lip of each hull to keep the crossbar in place and keep the boat rigid. This bolt just has a nylock nut on the underside of the hull lip. Similarly, there is a bolt that is threaded up through the inboard lip of the hull. This bolt will probably require a 5/8" allen wrench. This bolt threads into a casting that is riveted inside the forward crossbar, and also holds the crossbar in place and keeps the boat rigid. Either of these bolts should be replaced immediately if broken, or your hulls could be badly damaged.
If the inboard bolt has sheared, you will need to take off the forward crossbar to fix it. Remove the mast and trampoline. Remove the nuts on the tie rod. Remove the 4 bolts that hold the crossbar to the hulls (1 in the outboard lip and 1 in the inboard lip on each hull). Lift the crossbar off the hulls. If the bolt has sheared, you will need to remove the end casting, then drill out the rivets on the casting for the inboard bolt. Remove both castings and replace the inboard casting. Rivet the new casting back in place, then reassemble the boat. Also note - any loose rivets on the boat ought to be re-riveted anyways, particularly the rivets in the mast step and crossbars.
Though it may sound a little involved, it's really not a big deal. drill rivets with a power drill and a hardened 3/16" drill bit. The front inboard support casting kit will be ~$80. The rivets will be a few bucks (make sure you get the right ones!) and a hand riveting tool is ~$30. Get the heavy duty one from harbor freight, it'll make your work much easier!
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