Just measured my original plastic covers on my 73. Looks to me like the base (bottom side of the cover) is 1". There is the thickness of the plastic which makes the inside the cap 3/4". The top is 5/16". I would think you might find something that might work at a good hardware store? The ones on Ebay I believe are $18 with shipping seems a little high (ok a lot high) for two plastic caps, but if you just got to have them?
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