help with clutch slave cylinder, please

[jrt]

Evening , I'm trying to fit the slave rod over the clutch lever ball but no amount of force is making it fit, all I've managed to do is knacker my left hand. Does anyone have any tips for fitting them together, thanks
E D I T just measured the inner diameter of the old [plastic]socket 14mm and the new[metal with plastic inner] one 11mm also the rod on the new one is 90mm long and my old one is nearer 105mm. When stood next to each other with the piston down they are both the same length and according to various retailers this is the right one.
1983 wbx 1900 petrol 5 speed. Can anyone point me in the right direction please?
David

[Aidan]

it doesn't go over the ball/nipple unless it is the long black plastic end, the metal one with the nylon cup should sit on the ball/nipple nice like a easy socket joint and is preferable imho, dadge of lube

[jrt]

Well I never , thanks for that, it's the first time i ‘ve changed one.
David