cobee 50 Pieces Fountain Pen Balck Ink Cartridge, Fountain Pen Ink Refills for Calligraphy Pen 2.6 mm Bore Diameter(2.6mm)

At first I thought I bought the wrong size but I realized the only difference is actually the length and it worked out

If you are using this for the first time with a pen be sure that the cartridge can rest on the end of inside of the pen barrel. These do not grip the metal piece that pierces the cartridge, and thus will not stay in place unless they fit exactly. If they fit your specific pen then a great value, but if the cartridge does not grip the interior piercing piece I would be concerned about cartridge leaks.

Not Suitable. Even thought the listing showed detailed dimensions of the cartridge’s interface diameter, it didn’t show the dimension (length) of the barrel of the interface. It is nearly twice as deep as a standard Parker refill, so when inserting, the pen will not pierce the seal and allow ink to flow…The cartridges arrived on time and in a vacuum-sealed bag by ultimately we’re not useable in either my Parker nor Rotring fountain pens, but a no-name scholastic pen I had so they were not a total waste. The ink is permanent and nicely black.

Ordered a cheap pen from the same brand to give it a try and it ruined my ledger book. Horrible product, don't know if the pen or the cartridges are defective, or maybe both? Will be returning.

I have two 2.6 mm fountain pens, and neither are taking these cartridges. The ones I usually get "click" into the pen as it pierces the bore. These do not do that. They sort of fit, but the bore is not secure so I will not be using these. Shame too, because the price is great. Oh well. Too much trouble to return. I'll have to see if I can use these some other way?