You need to mill something. These bases are designed to accept metal bars from the same manufacturer, not standard 4x4 bars. So that means the inside size is 3 3/8, not 3 1/2, let alone 3 9/16, which is usually a true 4x4 size. The client didn't want me tearing up their deck to attach the poles to the joists. I didn't want to do that either, as decking screws (listed as stainless) tend to rust and break unless they're stainless steel, making removing the old decking risky. These bases fit the bill and while not as strong as wooden locks secured to a beam they are still almost strong and I secured them straight down with two wooden locks aligned with the beams. Photos are included so you can see what I had to do to prepare the 4x4s. Use a carpenter to taper the ends, then a router because the holes where the screws will go are about 3/16 deep.
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