In case anyone is looking for this information in the future, these are Lance Cleats and were commonly used on Hobie 16s for a while. Lance Cleat StarboardI just purchased a 1980 DC15 a few days ago. It's in okay condition but has some things that need attention. One thing that needs to be replaced are the combination roller/cam cleats that are on the tiller for the rudder uphaul and downhaul lines. One of them works okay but the other one is completely corroded and need to be replaced.
Does anyone know where this part can be found or have a suggestion for something else similar they've used for this purpose?