Cartriges for SOLO Ink Pen. 
International standard size 2.6mm (7/64 inch) bore diameter.
Sepia color, non-waterproof - can be washed out by water, but retain the visible line.
The package includes 10 cartridges.
Cartridge length: approx. 38mm (1 1/2 inches); 
Cartridge Diameter: 4-6mm (5/32 - 15/64 inch);
Bore diameter: 2.6mm (7/64 inch)