Ballpoints · Plate 15 / 23
uni (Mitsubishi Pencil Co., Ltd.)
uni-ball Signo UM-151
The barrel carries UM-151, not "DX" — the export designation does not appear on the object itself.
ThDag1453, Wikimedia Commons · CC BY-SA · commons.wikimedia.org
The Signo UM-151 is a capped gel pen with a 0.38 mm ball and pigment ink on a UMR-1 refill. In the Japanese catalogue it appears as uni-ball Signo Gokuboso 0.38 mm, factory name UM-151. In international circulation it goes by a different name, and that is the first thing to know about it.
The letters DX do not exist in Japan
"Signo DX" is an export designation used by Mitsubishi Pencil's Singapore company. The string "DX" never appears on the Japanese product page — against sixty-six occurrences of "UM-151" itself. Searching Japanese sources for "Signo DX" is therefore fruitless, and searching English-language sources for "UM-151" hits half the material.
The second storey of the naming problem concerns the 1990s. In Mitsubishi material from that period the catalogue number was written VM-151, not UM-151. It is the same article: the company's January 1998 page lists an item numbered VM-151.22 with JAN code 4902778 581933, while today's manufacturer page shows UM151.22 in the same colour under that same code. Searching 1990s archives means typing the old number.
Three widths, one name, three refill codes
One barrel serves three ball diameters sold under separate factory names: UM-151 (0.38 mm), UM-151-28 (0.28 mm) and UM-151-05 (0.5 mm). This entry concerns the 0.38 mm version, the only one available at launch.
The refill codes are built so as to invite mistakes: the digit after the hyphen is the ball diameter, and its absence means the default 0.38 mm. UMR-1 is 0.38, UMR-1-05 is 0.5, UMR-1-28 is 0.28. The maker assigns the UMR-1 to two bodies at once — the UM-151 and the UM-151-05 — so in the 0.5 mm body the line width can be changed by swapping the refill alone. Not the other way round: the UMR-1-28 is assigned to the UM-151-28 only.
The refill is 115 mm long and 5.4 mm across. It is a Signo-proprietary format matching no international standard — there are no other-brand substitutes and no point in looking for them by similarity of length.
The launch date comes from a document
July 1996 is not a reconstruction here. The maker's release of 30 May 2017 gives, in a single table, the trade name, the factory name UM-151, the 0.38 mm diameter and the sentence 1996年7月に発売以来. The July 2008 release confirms it independently: 1996年7月発売以来12年間. The model is also listed in the company chronicle under 1996.
Continuity of sale can be checked on a single number — the same barcode describing the same colour from January 1998 to today. Thirty years of the same trade article, with no discontinuation marking.
The rest of the timeline is short and comes entirely from releases: March 2003 adds the 0.28 mm version, July 2008 the 0.5 mm version and six new colours for the base variant, June 2017 twelve more colours, bringing it to thirty-one.
Canon, with a caveat
The model holds first place on The Pen Addict's Top 5 Micro Gel Ink Pens list, in a section updated on 21 October 2025. The same outlet has reviewed it since January 2008 — seventeen years of continuous presence.
We recorded this as secondary rather than primary evidence, for a specific reason: the list's author runs a company that sells a body for this model's refill. That does not make the recommendation untrue, but it does make it not disinterested, and the rubric should see that. An independent review carrying the model number in its title was published by Gourmet Pens in July 2011.
What we do not give
The barrel diameter. The documents disagree: the maker's export card says 10.3 mm, the Japanese Askul catalogue 11.4 mm with a maximum of 11.5 mm. More than a millimetre of difference is too much to average or to pick between arbitrarily, and we found no third independent measurement. The field stays empty. The 137.8 mm length and 11.5 g weight go in, because two sources confirm the length independently.
The designer's name. Neither the product page, nor the 2003, 2008 and 2017 releases, nor the company chronicle names whoever designed it.
A counterfeit warning, though it is a standard item in this section. We searched in Japanese and in English — Mitsubishi Pencil publishes no statement about fakes of this model, so there is nothing to cite.
Two out of seven: longevity and enthusiast canon. There is no award, no technical first, no sales figure. The only priority claim in the entire documentation — 世界最小, the world's smallest 0.28 mm ball, from the 2003 release — concerns a variant under a different factory name, is the maker's own declaration, and has no patent attached to it.
Specification
- Introduced
- 1996
- Status
- in production
- Category
- gel
- Designed in
- JP
- Mechanism
- capped
- Cross-section
- round
- Materials
- AS plastic (barrel), elastomer rubber (grip), stainless steel (writing tip)
- Length
- 137.8 mm
- Diameter
- no data
- Weight
- 11.5 g
- Market tier
- entry
Refill
- Standard
- uni UMR-1 (Signo)
- Factory code
- UMR-1
The UMR-1 refill: 115 mm long, 5.4 mm across, 0.38 mm ball, pigment gel ink. It is a Signo-proprietary format matching no international standard and no Parker G2 — there are no other-brand substitutes and none should be sought by similarity of length. The naming is a trap: the digit after the hyphen is the ball diameter, and its absence means the default 0.38 mm. UMR-1 is 0.38 mm, UMR-1-05 is 0.5 mm, UMR-1-28 is 0.28 mm. The maker assigns the UMR-1 to two bodies — the UM-151 and the UM-151-05 — so in the 0.5 mm body the line width can be changed by swapping the refill alone. Not the other way round: the UMR-1-28 is assigned to the UM-151-28 only.
Legend rubric
Criteria met 2 of 7
A model qualifies on at least two criteria. Every criterion marked as met must cite a source.
Longevity
metprimary sourceThirty years from July 1996 against a twenty-five-year threshold. Two independent maker's releases confirm the date, and continuity of sale can be checked on a single number: the JAN code 4902778581933 described a uni-ball Signo Gokuboso Brown Black item numbered VM-151.22 in January 1998, and today describes UM151.22 in the same colour. The same trade article under the same barcode for thirty years. The product page carries no discontinued marking.
Mitsubishi Pencil — komunikat prasowy: 『ユニボール シグノ 極細0.38mm』新色12色追加 (30.05.2017) · Mitsubishi Pencil — komunikat prasowy o dodaniu 0,5 mm do serii 極細 (lipiec 2008, archiwum Wayback) · ユニボールシグノ トラディショナルカラー — archiwalna karta Mitsubishi z 26.01.1998 (numeracja VM-151) · ユニボール シグノ — aktualna karta produktu (Mitsubishi Pencil)
Design recognition
not metThe iF, Red Dot and Good Design databases and the holdings of design museums were searched. The model appears in none of them. The maker claims no award for this entry — not on the product page, not in the 2003, 2008 or 2017 releases, and not in the company chronicle.
Technical first
not metThe only priority claim in this model's entire documentation reads 世界最小 — the world's smallest ball at 0.28 mm — and comes from the maker's release of 4 March 2003. We do not count it, for three reasons at once: it concerns a variant under a different factory name (UM-151-28) rather than this entry; it is the maker's own marketing declaration with no independent corroboration; and no patent accompanies it, none having been found. The twin-ball mechanism described in the 2003 and 2008 releases as protection against ink backflow is likewise not claimed by the maker as a first.
Mitsubishi Pencil — komunikat prasowy: 『ユニボール シグノ 超極細』 0,28 mm (04.03.2003, archiwum Wayback)
Cultural footprint
not metA trace in film, television, historic events and non-design museums was sought — nothing was found. The model is ubiquitous in Japanese stationery, but ubiquity is not a cultural footprint in this rubric's sense.
Scale
not metNo public units-sold figure exists. In the releases found the maker gives only first-year sales targets for the new 2003 and 2008 variants — a commercial plan for a derivative, not a result for the base model, so it is not evidence of scale.
Enthusiast canon
metsecondary sourceThe model holds first place on The Pen Addict's Top 5 Micro Gel Ink Pens list, in a section updated on 21 October 2025, with the identification "The DX, also known as the UM-151". The same outlet has reviewed it since 11 January 2008 — seventeen years of presence at one address. We lower the evidence to secondary strength because of a conflict of interest: the list's author, Brad Dowdy, runs Spoke Design, which sells a body for the UM-151 refill, so he is not a disinterested party here. An independent review carrying the model number in its title was published by Gourmet Pens in July 2011.
The Pen Addict — Top 5 Pens, sekcja „Top 5 Micro Gel Ink Pens" (aktualizacja 21.10.2025) · The Pen Addict — Review: Uni-Ball Signo DX 0.38mm (11.01.2008, Brad Dowdy) · Gourmet Pens — Review: Uni-Ball Signo DX (UM-151) 0.38 mm Gel Ink Pen (11.07.2011, Azizah Asgarali)
Practice influence
not metNo market of parts made for this model was found, nor a documented repeatable modification culture, nor institutional adoption. Third-party bodies accepting the UMR-1 refill exist, but that is a market for the refill, not for this pen — and evidence for this criterion may not be an editorial recommendation either, which is what the canon rests on.
Where to buy
We do not list prices. We list a market tier and the date each link was last checked.
- 三菱鉛筆オンラインショップ (oficjalny sklep producenta)JPmanufacturerverified 08/17/2026
- UNI SINGAPORE (Mitsubishi Pencil Company Private Limited) — karta produktuglobalmanufacturerverified 08/17/2026
- Cult PensUKspecialistverified 08/17/2026
- Yoseka StationeryUSspecialistverified 08/17/2026
- Stationery Palglobalspecialistverified 08/17/2026
- アスクル (Askul)JPspecialistverified 08/17/2026
- Amazon.plPLmarketplaceverified 08/17/2026
Related models
Sources
- 01Mitsubishi Pencil — komunikat prasowy: 『ユニボール シグノ 極細0.38mm』新色12色追加 (30.05.2017)
manufacturer · accessed 08/17/2026
『ユニボール シグノ 極細0.38mm』シリーズは、1996年7月に発売以来、国内外で安定して人気のある、当社ゲルインクボールペンシリーズのロングセラーアイテムです。／【商品概要】商品名 ユニボール シグノ 極細0.38mmボール／品 名 UM-151／ボール径 0.38mm
- 02Mitsubishi Pencil — komunikat prasowy o dodaniu 0,5 mm do serii 極細 (lipiec 2008, archiwum Wayback)
manufacturer · accessed 08/17/2026
ゲルインクボールペン『ユニボール シグノ極細』シリーズは、1996年7月発売以来12年間にわたり国内外で安定した売上を続けている…／『ユニボール シグノ極細』シリーズの従来ラインナップはボール径が超極細0.28mmと極細0.38mmの2種類のみでしたが…／■品 名：UM-151-05 ■ボール径：0.5mm
- 03Mitsubishi Pencil — komunikat prasowy: 『ユニボール シグノ 超極細』 0,28 mm (04.03.2003, archiwum Wayback)
manufacturer · accessed 08/17/2026
世界最小ボール径0.28mmのゲルインクボールペン新登場／■商品名：ユニボール シグノ 超極細 ■品 名：UM-151-28 ■ボール径：0.28mm ■リフィール：UMR-1-28
- 04ユニボール シグノ — aktualna karta produktu (Mitsubishi Pencil)
manufacturer · accessed 08/17/2026
ユニボール シグノ 極細 0.38mm ブラウンブラック／インク色 ブラウンブラック／ボール径 0.38／品名 UM-151／注文コード UM151.22／JANコード 4902778581933
- 05ゲルインクボールペン替芯 — strona wkładów (Mitsubishi Pencil)
manufacturer · accessed 08/17/2026
UMR-1 — ボール径 0.38 — 適合商品: ユニボール シグノ 極細 UM-151, ユニボール シグノ UM-151-05；UMR-1-28 — ボール径 0.28 — 適合商品: ユニボール シグノ 超極細 UM-151-28
- 06uni-ball Signo DX UM-151 | UNI SINGAPORE (Mitsubishi Pencil Company Private Limited)
manufacturer · accessed 08/17/2026
Size / Weight 1.03 cm x 1.50 cm x 13.78 cm / 11.5 g；Nib Size 0.28mm 0.38mm；Barrel Plastic (AS), Elastic rubber grip；Tip Stainless steel
- 07ユニボールシグノ トラディショナルカラー — archiwalna karta Mitsubishi z 26.01.1998 (numeracja VM-151)
manufacturer · accessed 08/17/2026
ユニボールシグノ極細 ブラウンブラック｜VM-151.22｜150円｜4902778 581933
- 08Signo — lista produktów marki na oficjalnej witrynie uni-ball UK
manufacturer · accessed 08/17/2026
uni-ball Signo Gel Grip UM-151S
- 09The Pen Addict — Top 5 Pens, sekcja „Top 5 Micro Gel Ink Pens" (aktualizacja 21.10.2025)
community · accessed 08/17/2026
uniball Signo DX 0.38 mm - The reigning champion for several years. The DX, also known as the UM-151, is the micro gel ink pen I compare all others to. … (Updated 10/21/2025)
- 10The Pen Addict — Review: Uni-Ball Signo DX 0.38mm (11.01.2008, Brad Dowdy)
community · accessed 08/17/2026
The more I use this pen, the more I like it, and I may like the 0.28mm model even better.
- 11Gourmet Pens — Review: Uni-Ball Signo DX (UM-151) 0.38 mm Gel Ink Pen (11.07.2011, Azizah Asgarali)
community · accessed 08/17/2026
Review: Uni-Ball Signo DX (UM-151) 0.38 mm Gel Ink Pen
- 12Cult Pens — Uni UMR-1 0.38mm Gel Roller Refill (wymiary wkładu i dopasowanie)
retailer · accessed 08/17/2026
Refill for Uni-Ball Signo DX (UM-151), Signo UM-120 and Signo Gel Grip (UM-151S) rollerball pens. Extra-fine 0.38mm nib. 115mm long, 5.4mm diameter.
- 13アスクル — ゲルインクボールペン ユニボールシグノ 極細 0.38ミリ 黒 キャップ式 UM151.24
retailer · accessed 08/17/2026
軸径 11.4mm／長さ 137.8mm／最大軸径 11.5mm／ボール径 0.38mm／メーカー品番 UM151／タイプ キャップ式
- 14三菱鉛筆のあゆみ — kronika firmowa, wpis pod rokiem 1996
manufacturer · accessed 08/17/2026
新水性ボールペン「ユニボールシグノ極細」…発売