I'm wondering if it would be legal to produce a custom piece for Lego Technic and sell it? The piece features 4 compatible connection holes for Technic pins. From what I've researched in the Lego Technic patents, the claim (in the first sentence of each patent) applies to "sets" not individual parts. Here are the patents:
Does anyone know if there are specific patents covering the pin hole system?
Note: I would of course make sure to use my own designs and not copyright infringe on any of their trademarks regarding packaging, marketing etc.