This is the plate our diamond roundup calls “the diamond plate to buy if you are buying one,” and it has been recommended on four pages of this site without a review of its own. That is overdue, because a DMT plate is one of the few sharpening tools whose maker publishes almost everything you would want to know — the abrasive in microns and mesh, the plate’s dimensions to the hundredth of an inch, the break-in behavior, the care routine, the expected life and the guarantee — and a review that reads all of it is more useful than one that describes the feel of a plate we do not own. Two things about it are less than ideal, and both are in the model number.
What DMT actually publishes
The product page for the W8FCNB states two abrasive grades on one plate: “Coarse” at “45 micron / 325 mesh” and “Fine” at “25 micron / 600 mesh,” on a “micronized monocrystalline diamond surface.” It is described as a “precision flat, double surfaced sharpener guaranteed to provide consistent, even sharpening every time,” to be used “dry or with water,” and “Made in the USA.” DMT’s collection sheet gives the bare plate’s dimensions as 8 by 2.63 by 0.38 inches — about 203 by 67 by 10 mm — and lists the with-base version of the same plate, the W8FC-WB, at 12.125 by 4.625 by 2 inches overall.
Those micron figures are the reason to buy a diamond plate rather than a stone for the coarse end. A water stone’s grit number is a manufacturer’s label on a bonded abrasive that wears and dishes; a diamond plate’s micron figure describes particles fixed to a steel plate that does neither. DMT’s color-coded chart, reproduced by the specialist retailer we cite, puts the rest of the range around this plate: Extra-Coarse 60 µm / 220 mesh below it, Extra-Fine 9 µm / 1200 mesh above. The W8FC covers the middle two. What it does not cover is a finish — 600 mesh is the grit a kitchen edge is worked at, not polished at, and the registry card says so.
The interrupted surface, from DMT’s own mouth
The DuoSharp’s polka-dot face is its signature and the thing most buyers ask about. DMT’s FAQ explains it plainly: the dots are “slightly recessed,” so the steel debris (swarf) falls away from the working surface instead of building up on it; the continuous-surface Dia-Sharp line exists because a solid face is “perfect for small-pointed tools.” That is the whole trade-off in two sentences. An interrupted plate keeps cutting through a long session on a hard knife because it does not clog; a continuous plate is the safer surface for a very fine tip, which can drop into a hole on the interrupted plate. DMT also sells a DuoSharp Plus (WM8FC) that carries both an interrupted area and “an additional continuous diamond surface for sharpening small and pointed tools” on the same plate; it was listed as sold out on DMT’s store when we checked, as was the W8FCNB itself. Our diamond stone vs whetstone page has the wider argument.
Break-in, care and how long it lasts — DMT’s numbers, not ours
Three things about diamond plates that surprise first-time buyers are all answered on DMT’s FAQ, and they are worth quoting rather than paraphrasing.
- It will feel too coarse at first.“When you first use your DMT sharpener, the diamond surface will seem aggressive in nature; the diamond sharpener will smooth after initial sharpening with no impact to long term performance. Your first few sharpenings are the break-in period.” Do those first few on a knife you do not care about.
- Water or nothing.“DMT recommends you use DMT products dry or with water only.” Cleaning is “after each use with water and wipe dry,” and “after several sharpenings, use a mild kitchen abrasive cleanser and a nylon scrub brush.” No oil, ever.
- It is not immortal.DMT’s own words: “When used properly, kept clean and stored dry, DMT diamond sharpeners will last a very long time. They do not last forever, but they last for several years.” That is more honest than the “lifetime” language most of the category uses. The plate never dishes and never needs flattening; what it eventually does is slow down.
And the guarantee, which is unusual enough to quote in full: “If your product fails to perform due to defects in materials or workmanship, we will replace it regardless of age.” Note what that does and does not cover — defects, not wear — but “regardless of age” is a phrase almost no one else in sharpening puts in writing.
One caution in DMT’s own advice
DMT’s FAQ says “We recommend sharpening at a 20-degree angle.” That is the right number for a German kitchen knife and the wrong number for a Japanese one, which arrives at 15–16° per side; on a gyuto, 20° puts a blunt secondary bevel on a thin edge. The FAQ’s next sentence is the one to keep: “sharpening at the proper angle is not as important as sharpening at a constant angle.” Hold whatever angle the knife came with, consistently. Our angle guide covers how, and the Japanese-knife sharpener page covers why the number matters more on hard steel.
The two problems, both in the model number
NB: no base. The listing we link is the bare plate. It is 8 by 2.63 inches of steel-backed diamond, 0.38 inches thick, and on a wet counter it moves. DMT sells the same plate with its bench-stone base as the W8FC-WB; the NB buyer needs a non-slip mat, a rubber-footed holder or a damp towel underneath, and should budget for one. It is a small omission with a large effect on how safe the plate is to use.
FC: Fine and Coarse, and nothing finer.600 mesh leaves a toothy, working edge. For a kitchen knife that is usable — it is roughly where a 1000-grit water stone leaves you — but it is not finished. A strop with compound, a 3000–6000 water stone, or DMT’s own Extra-Fine plate is the next step, and the strop roundup is the cheapest of the three.
How it compares
The three plates a buyer weighs this one against, on the figures each maker or listing publishes.
The DMT DuoSharp W8FCNB against the SHARPAL 162N, the DMT Dia-Sharp D8F and the Atoma 140| | DMT DuoSharp W8FCNB | SHARPAL 162N | DMT Dia-Sharp D8F | Atoma #140 |
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| Grits (mesh / µm) | 325 / 45 and 600 / 25 | 325 / 45 and 1200 / 12 | 600 / 25 only | #140 only |
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| Surface | Interrupted (polka-dot) | Continuous | Continuous | Continuous, replaceable sheet |
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| Plate size | 8 x 2.63 x 0.38 in. | 8 x 3 in. | 8 x 3 x 0.38 in. | Not published |
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| Base included | No (NB) | Yes — case lid | No | No |
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| Made in | USA | Not published | USA | Not published |
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| Guarantee (as published) | Replaced for defects regardless of age | Not published | Same DMT guarantee | Not published |
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| What it is for | Repair plus routine sharpening, one plate | Same, with a finer second side | Routine sharpening on thin-tipped blades | Flattening stones; heavy repair |
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Who should buy it
Someone who wants one plate that will do edge repair and routine sharpening on hard and soft knives alike, that never needs flattening, and that comes from a maker with a decades-long record and a written guarantee. Someone who owns water stones and wants a coarse plate to flatten them — the 325 side does that job, though the Atoma does it faster. Someone who sharpens a lot and values a face that does not clog.
Who should not: anyone who wants a finished edge off one tool (buy the SHARPAL for its 1200 side, or add a strop); anyone with a fine-tipped Japanese blade who would rather not think about the holes (buy the Dia-Sharp); and anyone who will not buy a mat or holder to go under an NB plate.
How we reviewed this
We do not own this plate and have not sharpened on it. This review reads DMT’s own product page for the W8FCNB, its DuoSharp collection sheet (for the dimensions and the with-base and Plus variants) and its FAQ, against DMT’s color-coded grit chart as reproduced by the specialist retailer we cite, the general reference on why plates stay flat, and the figures already compiled for the other plates we list. Where DMT publishes something, we quote it; where it publishes nothing (a weight, a warranty period beyond “regardless of age”), we say so. The listing’s ASIN was re-verified live via the Amazon Creators API on the review date under the title “DMT (Diamond Machining Technology) 8-Inch DuoSharp Bench Stone Fine/Coarse, (W8FCNB).” No price appears in this text: prices on this site come only from the live daily check and carry the date they were pulled. Our methodology sets out the rules in full.
