The link is pinned or bolted to the mast step casting. You align the mast base at the link and pin the link to a hole in the base casting. The two being connected by a "Hinge Link" for stepping.
Older models had a hook as part of the base and a pin in the step casting. You can drill out the pin. Cut off the hook and drill a hole in the base to update older boats.
Item #21380001 MAST STEP LINK KIT H14/16
Order from any Hobie Catamaran dealer. Step link instructions