cylinder attachment on H press

[giusseppe]

does anyone recognise this fitting to the cylinder in an H press. I have just purchased a used Enerpac press and am used to just using a saddle on the cylinder and cannot find any images of how tools can be fitted to this attachment or how to remove it. Any advice would be most welcome
thanks

 

[giusseppe]

this is the only picture I have found of the same attachment that I assume was threaded onto the cylinder.....but I dont know what the small round projection is for under the round plate. unless it is to centre anything that is bolted on.
Cannot seem to unscrew this either on my press