One of the corners of my mother's SuperFrame quilting frame corners has been broken for 10+ years, and it had been ridiculously expensive and nigh on impossible to find replacements for it due the brand no longer being in production (as far as I can find).

I designed and printed her a set of new ones. Don't know if these can fit other Quilting frame brands, and don't have a parametric version to adjust (modelled this in Blender), so your mileage may very.

Printed in PLA+ with 6 perimeters to ensure strength and 20% infill for some extra weight. Sink the model by 1mm into the build plate and use supports on the overhangs.