The original plans for the MiniCup calls for a 1/4-20 u-bolt to join
the gaff and boom so they can move relative to each other.
Unfortunately, the boom's thin metal has torn (after 4 yrs of use) so
the were going to separate. So, I got a piece of 2X4 and cut it to
fit into the end. I cut two pieces, drilled a hole lengthwise thru
each and inserted a long 5/16 bolt after I bent the shank near the
eyes slightly. I opened one of the eyes and joined the two eyes.
Then I glassed over eacjh of them to make em stronger and inserted
them into the spar ends and screwed them into place thru the
aluminum. It ought to be fairly strong.