Compiled from 6 sources; we haven't tested this product ourselves yet. How we research
Quick answer
The Tombow MONO Knock is a click-out, pen-style eraser from Japan's Tombow, holding a round 3.8 mm stick of MONO eraser in a clip-on barrel with a rubber grip. Tombow first sold it in Japan in November 1995. Refills come in packs of 4, and the holder sits in our $ band, under $5.
On this page10 sections
The MONO Knock, drawn in proportion (Tombow publishes no length).
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Notes on these facts
Made by Tombow Pencil Co., Ltd. (Tokyo); sold in the US by Tombow USA. Country of manufacture not stated: Tombow USA's product page and the Amazon US listing don't state a country of manufacture, and Tombow's Japanese site no longer has a product page for the MONO Knock. Check the package. Source. Price: example listing. Released: GetNavi's 2025 overview of Tombow's MONO line gives November 1995 for the MONO Knock 3.8; Tombow's own pages we found don't give a date.
Price bands are typical US retail, checked October 2026. Conversions to US dollars are approximate, at October 2026 rates (US$1 = ¥158 = ₩1,330 = NT$32.5 = CN¥6.7 = SEK 9.9 = DKK 6.7 = ₺49.6 = C$1.41 = A$1.43 = CZK 21.7; €1 = US$1.12; £1 = US$1.32; CHF 1 = US$1.21).
Key takeaways
Tombow USA lists the MONO Knock's eraser as round and 3.8 mm in diameter, wider than the MONO Zero's 2.3 mm tip.
Japan's GetNavi dates the MONO Knock 3.8 to November 1995; Tombow sells it in blue, green and pink.
Tombow's 2023 Japanese price list puts the holder (EH-KE) and its 4-pack refill (ER-AE) at ¥120 (about US$0.80) each before tax.
The blue MONO Knock's UPC is 4901991650341; the refill 4-pack's is 4901991650389, per Tombow USA.
Its Amazon US blue single listing showed 1,516 ratings on October 22, 2026.
What is the Tombow MONO Knock?
It’s a refillable eraser shaped like a pen: you click the end to push out a round stick of eraser, 3.8 mm across. Tombow, the Tokyo maker of the MONO eraser, has sold it in Japan since November 1995, according to Japan’s GetNavi.
“Knock” is the Japanese word for a click mechanism. The barrel has a pocket clip and a rubber grip, and Tombow’s Japanese blog says the eraser is firm, so it holds an edge for small corrections. On October 22, 2026, its blue single on Amazon US showed 1,516 ratings.
Tombow MONO Knock specs
Spec
Value
Maker
Tombow Pencil Co., Ltd. (Tokyo)
Model
EH-KE (holder); ER-AE (refills, Japan)
Eraser
Round, 3.8 mm diameter
Mechanism
Click (knock) advance
Body
Pen style, clip, rubber grip
Colors
Blue, green, pink
Refills
4 per pack
UPC
Blue 4901991650341 · refill 4-pack 4901991650389
Japan list price
¥120 (about US$0.80) before tax, holder or refills
Price band
$ (under $5)
Tip size, colors and UPCs are from Tombow USA; the Japanese codes and prices from Tombow’s 2023 price list. Tombow doesn’t publish the length or weight in the sources we found.
How does the MONO Knock compare with the MONO Zero?
The Knock has a thicker stick for small patches; the Zero is a fine-tip eraser for single letters. Both are click-out holders from Tombow, but they take different refills.
For erasing a whole page, a block eraser such as the Tombow MONO or the Pentel Hi-Polymer is faster. The Knock is for the work in between: a word in a planner, a corner of a sketch.
What is the MONO Knock good for?
Erasing a word or a small patch without disturbing what’s around it. At 3.8 mm, the round tip is a little narrower than a 6 mm ruled line, so it lifts one word in a planner or a mistake inside a sketch’s outline.
Tombow’s Japanese blog calls the eraser firm, and GetNavi says it resists snapping. We haven’t yet compared it with the softer MONO block.
How do you refill the MONO Knock?
Pull out the spent stub, drop in a new stick and click it forward. Tombow USA sells the refills in a 4-pack, and in Japan they are the ER-AE. Each stick is the same 3.8 mm round eraser.
Click out only a few millimeters at a time. A long, thin stick pressed hard can bend or snap.
Is the MONO Knock worth it over a block eraser?
Yes, if you erase small areas often and want the eraser to stay clean in a bag. The stick sits inside the barrel and the clip keeps it in a pocket, so it doesn’t pick up dirt the way a loose eraser does.
A click eraser also keeps a narrow, clean edge as it wears, while a block’s corners round off. Pentel’s Clic Eraser is a similar click-out idea from another Japanese maker.
Where is the Tombow MONO Knock made?
Tombow doesn’t say on the pages we found. Tombow USA’s page and the Amazon US listing give no country, and Tombow’s Japanese site no longer has a product page for it, though its 2023 price list still includes the EH-KE.
Tombow is a Japanese brand based in Tokyo. The MONO name started with the MONO 100 pencil of 1967, whose giveaway eraser became Tombow’s best-known product, and its blue, white and black stripes now mark the whole family.
Frequently asked questions
How do you use a Tombow MONO Knock eraser?
Press the clip end to push the eraser out a little at a time, erase, and keep clicking as it wears. Pressing hard with a long length showing can bend the thin stick.
How do you refill a Tombow MONO Knock?
Buy the MONO Knock refills (ER-AE in Japan), sold 4 to a pack, and load a new stick into the holder when the old one runs out. Tombow USA sells the 4-pack separately.
Is the MONO Knock the same as the MONO Zero?
No. The MONO Knock holds a 3.8 mm round stick for small areas; the MONO Zero holds a 2.3 mm round or 2.5 × 5 mm rectangular stick for single letters and lines.
What colors does the MONO Knock come in?
Tombow USA lists blue, green and pink barrels. All take the same refill.
Does the MONO Knock erase pen?
No. It's a plastic eraser for pencil and colored pencil. Ink needs a sand eraser or correction tape.
How much does the Tombow MONO Knock cost?
It sits in our $ band, under $5. In Japan, Tombow's 2023 price list puts the holder at ¥120 (about US$0.80) before tax.
Is the Tombow MONO Knock made in Japan?
Tombow doesn't say on the pages we found. Tombow is a Tokyo company, so check the package for the country of manufacture.
