Today, I was taking apart a mast pipe in a home-made stub tower and this spacer fell out: It looks like about a hundred years ago, somebody was using the same method Windy was suggesting.
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I drill a small hole fromt he inside out, then grind a flat spot on the point and drill outside in if I am in the field. If I am in the shop I clamp it in the Bridgeport and use an endmill, easy peasy.