I changed cartridge to converter for fountain pen.
My Fountain pen is PILOT PRERA(Amazon.co.jp).
This cartridge i bought is PILOT CON-50(Amazon.co.jp).
Ink is PILOT Black ink(Amazon.co.jp).
1. Remove old empty cartridge.
2. Turn the knob to the left (counterclockwise).
3. Push the converter into the body of the pen.
4. Immerse the nib fully in the ink.
5. Turn the knob to the right (clockwise) to fill converter with ink.