*This feed was developed about a couple of weeks ago,
so all the shipped pens recently are equipped with this feed.
Upgraded from Eureka ebonite feed 4G v2,
upgraded features of the 4G v3:
- more slanted cut towards the front
- air channel modded for maximum flow while achieving high stability
- ink channel and air channel machined deeper
- frontal area higher precision, allowing perfect horizontal balance of the nib
- better compatibility with eureka nibs (overall nib groove shape)
