Most Jinhao fountain pens can use an international sized ink cartridge with a bore size of 2.60mm. This is the only size of Jinhao ink cartridges we presently sell. However, I learned today that a few Jinhao fountain pens (including some of the 619 model) need ink cartridges with a bore size of 3.4mm. 

So the Jinhao ink cartridges we sell (bore size of 2.60mm) do not in fact fit all models of Jinhao fountain pens. 

Note 1: this also means the syringe converter for bottled ink is a different size in some Jinhao models.  
Note 2: the bore size is the inner diameter of the end of the cartridge/convertor.