Pilot Hi-Tec-C Slims Gel Ink Multi Pen Refill - D1 - 0.4 mm - Black

Perfect. Not too scratchy but not too smooth which causes bad handwriting.

I have 3 Zebra Sharbo X LT3 (green, orange and, gray ). They fit perfectly. This pen is just magnificent.

Excellent refill. Thin line, not too smooth that could make your writing bad and not too scratchy which makes you slow and inconsistent like the 0.3.

A nice quality refill. Tried it to get the Hi-Tec-C experience in a Sharbo X multipen. Unfortunately, it's too loose and won't fit snug. The refill will fall out of the pen if your try to use it. A remedy was to put a small piece (2mm long) )of scotch tape on the top of the refill, and it will fit with friction. The ink is not as good as the Sharbo X refills (not as water-resistant), but will be smoother to left-handed writers.