Anyone recognise this type of fitting to a cistern?

[DonkeyApple]

Replacing the ballcock and valve stem on a cloakroom cistern and the plastic thread into the external metal piping is t filling me with confidence. There is no real means on the plastic side with which to get purchase to screw it into the external metal piping so I'm assuming that it's the nut at the end of the metal pipe that is what one turns to ensure a tight fit, however a fair few years of paint doesn't make this immediately clear so before I start holding the the joining nut and seeing if the end is meant to rotate freely and allow the tightening of the thread I thought I'd ask the professionals

[Brinyan]

Whoever connected the pipe to the fill valve originally (many years ago), has used a female copper to iron coupling. Not the best method, but the nut at the bottom of the fitting will turn clockwise to undo, but hold the upper part of the fitting when undoing the nut. The copper to iron fitting will also unscrew clockwise from the fill valve.
Maybe best to then cut the pipe back & connect the new valve with a flexible braided hose-type tap connector.

[g7jtk]

It is a 1/2” female iron to 15mm straight in brass. The manufacturers name and size will visible be on the end of the compression nut once the paint is removes.