Coventry Quick Change Tool System | Model Engineer
There's a dog (or two?) on the face of the "master shank" that engages with a slot(s) in the holder. Nice system in principle but expensive, not so easy to change as first appears, and they eat daylight between spindle and work. My Novamill came with an Easychange BT30 shank and a couple of ER16 collet holders, but I quickly got a couple of ER16/BT30 chucks and later some BT30 split collets to make better use of the limited daylight.
Source: model-engineer.co.uk