LOL.
The chrome adapter is supposed to be threaded into the body of the diagonal in the place of the SCT-threaded one. It is not supposed to be threaded into the ring on the SCT attachment.
First, unscrew the SCT part with its ring, then thread the chome barrel into the diagonal body. By so doing, you convert an SCT threded diagonal to a refractor style and it yields a larger clear aperture through the diagonal.
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