I have lots of metal terridons to mount and paint but find the clear plastic stems have a tendacy to break would I better of removing the end and drilling a bigger hole or using a different type of stem
It's certainly worth drilling a bigger hole to stick your Terradons to the stems themselves rather than the minuscule pegs on the ends. Also what sort of container are you using to store them, out of interest? Do you have much in the way of foam around them? Might be worth investing in better containers that stop them rattling around and breaking the stems if they're currently not packaged well enough.
I use a long thin nail painted black. Much stronger and less costly than more plastic rods. Just have to drill carefully.