Is it legal to sell a custom element that provides a Technic pin connection? 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: 


https://www.google.com.gi/patents/US5964635
http://www.google.com/patents/US6736691


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.
I am not a lawyer, and I recommend you consult one before you start dropping money on injection molds, but as far as I know this should be fine. SBrick definitely already does this:



In most jurisdictions, patents have a term of 20 years or less. The Technic pin connection dates back to Expert Builder in 1977, so it is not patent encumbered at this point.

The two patents that you linked to from the late 1990s appear to be for ZNAP, which uses a different connection system: