Wood beams can be joined in different ways. Traditional joinery
uses mortise and tenon connections with wooden pegs drilled through
to hold the beams together. Steel plate joinery uses metal plates
and bolts.
Simpson is a company that makes simple fasteners for wood
connections.
Steel connections can be made to order through a local steel
fabricator. the important thing is to make sure that the joinery is
strong enough to carry the loads that the beam carry. Often the
help of a professional engineer is required to size the beam and
connections whether wood or steel is used.