Hi Simon - its the mono one that is most commonly used for guiding, sometimes for lunar and planetary imaging. I am not sure whether it has a letter designation like V or T - though I don't think so. If you have a look at
Gama's site you will see them there.
Just so you know - another user PM'd me expressing interest about 10 minutes before your post - but I will keep you posted on whether it is sold or not.
Cheers
Adam