Found this magazine description of the Self-Tying Ruger Patent Insulator. What is also interesting besides the self-tying groove design is the molding of the pin and insulator together with a slot at the bottom of the pin for a tab to anchor the pin. Reminds me of the Pyrex insulator/pin combination that Bob Berry found. Too bad this patent was never put into production or found in the wild.
Here is the patent information: http://reference.insulators.info/patents/detail/?patent=U367164