The rubber stoppers are for money boxes. I've made a few in the past but they didn't have a hole to remove the money easily.
Now I can make some new ones with stoppers. They will have to have some little feet to give clearance for the stopper but that's no problem.
My base slip has a Mason stain in it that has been discontinued. So I had to order two stains that I'll mix to make the discontinued one. Here is a CHART that may be helpful if you have found your favorite Mason stain has been discontinued.