The Uni-ball UMR-85E is the gel ink refill found in the Uni-ball Signo 307. It is the 0.5 mm version of the UMR-87E.
Uni-ball UMR-85E Gel Pen Refill

The Uni-ball UMR-85E is the gel ink refill found in the Uni-ball Signo 307. It is the 0.5 mm version of the UMR-87E.
The Uni-ball UMR-83E is the 0.38 mm gel ink refill sold in the Uni-ball Signo 307 pen.
The Uni-ball UMR-87 is the 0.7 mm gel refill found in the Uni-ball Signo 207 line of pens.
The Uni-Ball 207 Plus+ is an update to the popular Uni-Ball 207 gel pen. It was released in mid-2020.
The Pilot G2 Limited is a metal-bodied, executive pen based on the popular Pilot G2.
The Pilot G2 is a rollerball style refill designed to fit in Pilot G2 retractable pens. While not technically a standardized size, many refills are commonly referred to as being Pilot G2-sized or Pilot G2 compatible.
The Pilot G2 Pro is a variant on the standard Pilot G2 gel pen that features a slightly upgraded body, but it’s still essentially the same pen as the G2.
The Libretto is a rollerball-style pen that uses Pentel’s Energel gel ink refills. Pentel calls it’s a “Roller Gel” pen despite that not being a popular naming convention.
The Energel Pro Permanent, sometimes call simply the Energel Pro or Energel Permanent, is a variant of the Energel liquid gel pen that uses a permanent, waterproof pigment-based ink. The ink is quick-drying like that of all Energel pens, but it’s also waterproof, fade-resistant, and fraud-proof.
The Karas Kustoms Bolt is a metal, machined pen with a bolt-style knock. The current version of the pen is known as the Bolt V2, marking some slight changes between it and the previous version.
The Sakura Gelly Roll isn’t just a classic, great gel pen, it’s the original gel pen.
Arteza Gel Pens are super affordable gel pens that strongly resemble the Uni-ball Signo DX (UM-151). The Arteza gel pens are super popular on Amazon, where they have excellent reviews.
The Zebra Sarasa Grand is one of the best deals in the pen world. It’s a metal pen that uses Zebra’s excellent Sarasa gel link, and sells for under $10. It’s almost impossible to beat.
The Pilot Dr. Grip Gel is a popular pen that is known for its comfortable grip and wide availability. Dr. Grip pens are sold in ballpoint (the most popular type) and gel models, as well as a mechanical pencil.