I make them out of old maple shafts. I bought a pack of tenons once and after looking at them decided not to use them as the dimensions were wrong. I like to install at least 1" deeply and then have 1" protruding. I also make them slightly larger than 5/16" and turn one end as a good fit into the hole I bored in the shaft and leaving the protruding end large enough that it can be turned concentric to the shaft.