Data port cap for NSK calipers

[6PTsocket]

These were often sold as General/MG or Fowler but made by NSK in Japan. I picked them up at a flea market and they have worked great for years. They were pretty high end in their day. I remember MSC used to carry the data printer. The thing that bugs me is mine was missing the dust cover for the data port. I have tried to identify the connector for years but I think it may be non standard. A D-sub cap will not work. Does anybody recognize this connector?  The owner's manual shows there was a cap. I have contacted the companies that sold it with no luck. Thanks.

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