Good news, everyone. We have successfully completed our testing of the new gripper design compatible with the standard single-armed horn that comes with the DS3218 servo. The new gripper is now called rcr_gripper.stl, while the old gripper has been renamed to rcr_gripper_old.stl.
There is absolutely no need for the pink horn which used to be available on eBay, but has sold out. If you managed to purchase it while it was still available, then please print rcr_gripper_old.stl instead of rcr_gripper.stl.