Yes it's the Tak collimation scope. Gave me quite a fright, last time I fitted it to the 3" starlight focuser in my refractor. The brass compression ring, unbeknown to me, was a perfect fit into the recess of the 2" adapter........ When I came to remove it, I spent at least 10 to 15 minutes jiggling/pulling it, and I was starting to sweat over what the outcome would be. Luckily it came free, and I have not fitted it since. The recess is machined dead square, so I need to get a slope machined into it, to allow the compression ring to ride up and over.