Here ia a link to o ring source.
Use the Buna-n o rings. These o rings will not come apart nor will they leave black smudges and streaks where used. Std. o rings will.
I use these to hold the 2 pieces of a duck call together.
Std. 5/8 hole and the tenon just fits inside cut a grove the width of the o ring and as deep as needed to have some of the o ring above the tenon and this will be the friction fit to hold the two pieces together.
You just need to select the size that fits your need. you may want to put two on or whatever you need.