Uni-ball Signo RT1 UMN155-05 Retractable Gel Ink Rollerball Pen 0.5mm Green Box of 10

0.5mm. uni-ball's 2026 product catalogue lists the Signo RT1 in three widths, 0.38mm, 0.5mm and 0.7mm, and UMN155-05 is the 0.5mm version.

Because two colours run out of meaning quickly. Once black is the original and red is the correction, a third colour is the only way to show a second person has been over the page. Green is the usual choice for that, and for anything marked as passed.

Retractable. uni-ball's product page describes the Signo RT1 as an ultra fine retractable rollerball pen, so there is no cap.

uni-ball's website writes this width as UMN155-05, while uni-ball's 2026 catalogue uses a different pattern for the family, writing the finer 0.38mm pen as UMN-155-38. The website code UMN155-05 is the one for this 0.5mm pen.

One box of 10 uni-ball Signo RT1 UMN155-05 retractable gel ink rollerball pens, all in green ink, each with a 0.5mm line.

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