PILOT G2 Gel Refill (BLS-G2-7-B) - Black - Fine (0.7mm)

PILOT G2 Refill Fine Gel (BLS-G2-7-B) - Black - 0.7mm for PILOT G2 gel pens.

Available in black or blue ink.

Other rollerball pens accepting Pilot G2 refills:
Fit may not be perfect, but is acceptable for many users.
(if harvesting from a Pilot pen use the spring as well)
Faber-Castell Essentio, Hexo, Neo
Kaweco
Lamy 2000 (instead of M63) with a spacer such as trimmed plug off M63
Lamy Safari/Al-Star (instead of M63) with a spring or spacer 
Lamy Swift with refill end cap removed
Pentel Energel compatible pens (see below)
Pilot B2B, Dr Grip, G2 Edge, G2 Limited, Juice, MR
Retro 51 Tornado
Rotring 600
Sheaffer
Tactile Turn
Waterman