I seem to remember that, during wwII, the guys at some eastern US air force base found that they could solder a penny or a nickel into the center of a spark plug compression washer and then use it in a vending machine. The idea worked so well that it created a major problem for vending machine makers and operators of the day.
I found it! There is an extensive Popular Science article, "How Coin Machines Detect Phony Money" from March of 1962 that covers the "Philadelphia Quarter" or "Air Force Special". The penny was simply jammed into the spark plug gasket. I've plugged the link in here, but it's pretty long, so you will probably have to reassemble it yourself:
formatting link
Interesting to note: Within that pdf of the whole magazine, there's a one page ad for "American Machine and Tools". It shows an 8" tilting arbor table saw for $9.95. It's all there but the motor. I bought one at about that time and used it for many, many years, with a 1/3 hp washing machine motor that I had to reverse in a rather unconventional way.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.