Sailor fountain pen refill 0103

Product code
[Black 0.5mm]
：18-0103-120
[Black 0.7mm]
：18-0103-220
[Red 0.7mm]
：18-0103-230
[Blue 0.7mm]
：18-0103-240
[Black 1.0mm]
：18-0103-620
JAN code
[Black 0.5mm]
：49-01680-28037-8
[Black 0.7mm]
：49-01680-28031-6
[Red 0.7mm]
：49-01680-28032-3
[Blue 0.7mm]
：49-01680-28034-7
[Black 1.0mm]
：49-01680-28058-3
Specifications
Character width: extra fine, fine, bold
Tip: Stainless steel 0.5mm/0.7mm/1.0mm
Application: For oil-based ballpoint pens
Body size
φ2.3×67mm
Body weight
0.9g
package
celery pack
Size: 35 x 150mm (35 x 180mm when using header)
Weight: 3.3g

How to replace and refill the core