These unusual large screws are from a Balthaup (Germany) dining table,
(My child's "CSI credit card" there for scale :) )
The table's around 12? yrs old.
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You need a pin wrench (or pin spanner).
They come in fixed and adjustable types.
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Fantastic stuff - for the hordes of googlers also needing the spanner for this Balthaup table attachments:
indeed the "CRL pin spanner" is perfect. The pin size is exactly correct.
The pitch you can vary, but I was concerned the pin size itself may be wrong. if you have to buy a pin spanner with exchangeable pins, to cover all metric/imperial pin sizes, the only sets I found were 100+ bucks.
Fortunately this CR Laurence model which is only 10-20 bucks is perfect.
it appears to be known as a "spanner for Top Roller" in some markets.