All coins and tokens have an edge. If you pull out the change in your pocket or wallet, you’ll notice that some of the edges are smooth, like on a penny or a nickel, and some have little ridges (or reeds) like on a dime or a quarter.
Tokens are no different. When we mint coins/tokens, a blank metal disc is dropped into a collar. A collar is a ring that keeps the metal from squirting out the sides with it is struck with the tons of force needed to produce a die struck coin. The inside edge of the collar can be smooth or have ridges.
When the blank is squeezed between 2 dies, the metal is forced up in the dies (to create the image) and out into this ring, making the edge of the coin take on the shape cut into the collar.
How Making a Coin is Similar to Making a Waffle
Think about it similar to a waffle press – the batter takes on the shape of the press – whether it’s the “standard” waffle you get at the Waffle House, or one shaped like a death star or Mickey Mouse. Sometimes you put too much batter in and it oozes out the sides. A collar contains the metal and also gives it an edge – hence the reeded or plain.
See the rest of the post at https://www.osbornecoin.com/the-difference-between-plain-and-reeded-edge-coins/