Another mystery T-mount adapter

Here's another mystery lens-to-camera adapter -- similar to the other one I have listed -- but this time, I know what half of it is.

The lens side is a T-mount. The camera side is a three-tab bayonet mount -- very similar to the other one I listed. The diameters are almost the same, as are the dimensions of the bayonet tab, but not quite. Plus, this mount has a small tab which you can see in the photo -- probably to stop the rotation. The other mystery mount does not have this tab.

Any ideas?

Exakta?

Exakta has a MUCH smaller diameter bayonet.

Bet it's a Petri. The pin locates in the red hole and it has 3 lugs on the mount...

You nailed it. It's a T-mount to PETRI, for sure. Thanks.