When I grease by bike I notice the grease gun doesn't snap onto the grease nipple,,making it hard to get grease in ..Are they a different sizes?
Do i need to get a different gun ?..anyone know ?...thanks

 

The zerk fittings should be the same size. Only thing I can think of is the fitting is caked with dirt around the skinny part making it so the lock won't work. Make sure the fitting is super clean and try it again. That's the only thing I can think of. If grease still doesn't go in, you might need new fittings.