Used my new grease gun for the very first time yesterday


I think its because the gun is brand new and so the sprung clips at the end are very strong. I unscrewed the grease nipple so i could take it and the gun to the bench to give it some real force....still no luck

So anyway, while i work out how to separate those, i need to replace the grease nipple off the upper trunnion and i see that grease nipples are fairly cheap on ebay but does anyone know what size please?
Thanks
Matt
Ps: and if anyone has any ideas for the nipple stuck in the grease gun then pls shout
