I’ve used a regular grease gun on fittings like that – you have to hold it tight to the joint because it won’t stay on by itself. Take a piece of wire and clean dirt out of the hole first.
Dave
Those grease nipples are meant to be used with one of these type of grease guns. The harder you push on the pump, the tighter it gets on the fitting. This type comes in real handy for greasing shift levers where the nipple is recessed in the lever quite a ways.