Underwriter's knot -- safe wiring
I just repaired my 1940s-era radio that I thought had blown a tube. Turns out that the stupid plug (does not appear to be original) was not wired safely so the soldered wire got pulled out due to strain on the cord over time. Sure enough, when I opened it up, there was no Underwriter’s knot aka UL knot to be found. I made sure to tie one before re-soldering the wire so that it wouldn’t happen again.
This site has great graphics for tying your own if you happen to be wiring a light fixture or fixing the plug on a cord. Not only will it save your cord, it could save your life.
