[Boatanchors] Mystery round plastic discs

[John King]

I have two MYSTERY round plastic discs that appear to fit on a 1/4 inch shaft. 
The shaft holes have ridges as if they were to slip over a shaft that had ridges 
on it to keep the discs from slipping and rotating on the shafts. 


The discs are black plastic 2 3/16 " in diameter and 1/4 inch thick. Although 
they are solid discs the design has 4 triangular shaped flutes on each side. 
These showed up on my work bench and were found during a cleanup. The only piece 
of gear that I have worked on in that particular area is a Hallicrafters SX 71 
receiver.

Have any of you run across a piece of gear that has such plastic discs? Your 
assistance will be appreciated to assist in identifying these discs and the 
piece of gear they belong on. Thanks and 73, John, K5PGW