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The modified "U" shape of the model 565 spring clamp is designed to hold a 521-B spherical mount in a 560‑2 cup mount.  The 521-B may in turn hold a target or an alignment telescope's objective end.  Two small upturned clasps at the bottom of the spring clamp seat into recesses on the cup mount.  A thumbscrew provides sufficient force to clamp a spherical adapter in to the cup mount.