i used this thing called a nylon cup washer with internal diameter of 5/16" on my variable voltage bottom feeder
mod that iade out of a "c" battery box. it is similar to the drip cups on the monkeyboxx. looks a little tacky, but it is a plastic batter box
mod anyway. i am going to used the finishing washer on the wooden version i am currently making. thanks all of you for sizing guidance.