The lower panel of the mast tube is 14mm outside diametre high modulus tube.

A piece of 16mm tube forms the basis of the horizontal element of the joint.

It is glued in place together with pieces of 14mm sleeve that form the first telescopic taper element of the main boom and jib yard.

The intersection, where the mast passes through the joiner, is reinforced by simply wrapping carbon ‘tow’ around it as a way to prevent the tube fibres from splitting, and to provide a tensile link between the tube skins.
Five minute epoxy is used to hold the parts together as tow is laminated on.

The boom and yard are 12mm tube and they need not be glued into the 16mm and 14mm joint body.

This solution also requires no fittings and is arguably simpler to create than a joint with box section or foam sandwich booms.