Buy it if you own a serrated knife you intend to keep. The taper is the product: DMT publishes a 4.43-inch rod that narrows from 1/4 inch to 1/16 inch, which means one tool fits every scallop in a kitchen instead of one size of scallop. That single geometric fact is why this unremarkable-looking folding tool is the top pick on our serrated sharpener roundup and why most of what people own cannot do this job at all.
DMT’s own page for the fine Diafold Serrated describes a tool that “not only maintains serrated edges, but also serves as a mini-steel, gut hook sharpener, and conical file,” built on a “micronized monocrystalline diamond surface” in “fine diamond (25 micron / 600 mesh) for honing a razor sharp edge.” It is “convenient sized at 9 1/2” open and 5” closed,” the “folding plastic handles also protect the sharpener when not in use,” and “no messy oils are needed either, so you can sharpen dry or with water.” On provenance DMT is unusually specific: “Sharpener made in the USA, other components made in China.”
We do not own one and we have not worn one out; our methodology page says what we do instead. What follows is DMT’s published specification read against what a serrated kitchen edge actually needs — including the part of DMT’s own advice that does not apply to this tool.
Why a cone and not a rod
Serrations are not one size. A bread knife’s scallops are wide, a utility knife’s are narrow, and on many blades large and small gullets alternate along the same edge. A cylindrical rod has exactly one diameter: it fits one gullet size and bridges across every other one, which means it grinds thepoints of the teeth rather than the cutting edge recessed between them. Do that enough and you have a knife with a decorative wavy line and no bite.
A cone solves it by having every diameter between its two ends. DMT publishes those ends — 1/4 inch down to 1/16 inch — so you slide along the taper until the rod fills the scallop, then work there. The practical rule from the specialist guidance for this category is to position the rod so it fills the gullet without riding up onto the teeth, and the taper is what makes that possible on a whole drawer of different knives.
The second half of the geometry is the part most people get wrong, and it is not about the tool. As the specialist instruction puts it, “most serrated knives are chisel ground, one side is beveled, while the back is flat.” So you work the beveled face, inside each gullet, and you do not grind a new bevel into the flat back. The flat side gets deburring only, edge-trailing and very light — which is a job for a flat plate, not for this rod. That is why our serrated roundup pairs this tool with the D8F bench plate, whose continuous surface will not round the flat you are trying to keep flat.
Fine is the right grade, and DMT says why
DMT publishes a full color-coded grit table, which is the main reason we trust its grade claims: Extra-Extra-Coarse at 120 micron / 120 mesh, Extra-Coarse at 60 micron / 220 mesh, Coarse at 45 micron / 325 mesh (blue), Fine at 25 micron / 600 mesh (red), Extra-Fine at 9 micron / 1200 mesh (green) and Extra-Extra-Fine at 3 micron / 8000 mesh. This tool is the red one.
DMT’s own description of that grade is exactly the job here: it “restores to a fine edge any knife or tool that is slightly dull,” and DMT notes that “many of our customers consider the fine grit to be a medium/all purpose sharpener” and that “professional chefs and gourmet cooks work through to our finer grit models.” On a serrated edge that matters more than it would on a flat bevel: coarse diamond inside a gullet does not just sharpen the scallop, it reshapes it, and you cannot put the profile back. Fine removes enough steel to restore bite and not enough to redraw the tooth.
The Diafold Serrated against the other two tools our serrated roundup recommends, on published figures only| | DMT Diafold Serrated, Fine | Lansky Folding Tapered Rod | Chef'sChoice 15XV |
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| Format | Folding tapered diamond rod | Folding tapered diamond rod | 3-stage electric machine |
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| Abrasive grade published? | Yes — 25 micron / 600 mesh (Fine) | No — 'diamond', no mesh or micron | Diamond stages, no grade stated |
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| Tapered | Yes — 1/4 in. to 1/16 in. | Yes — not quantified | n/a |
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| Working length | 4.43 in. rod | Not published | n/a |
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| Serrated capability stated by maker | Yes — purpose-built | Yes — tapered serrated rod | Yes — Stage 3 only, per its manual |
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| Can restore a reshaped gullet | Yes, slowly | Unknown — grade unpublished | No — maintenance only |
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| Closed size | 5 in. closed, 9.5 in. open | Folds into handle | Countertop appliance |
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What it is like to live with
Three things about the format rather than the abrasive, because they are what decide whether a tool like this actually gets used.
The folding handle is the reason it survives.Loose diamond abrasive in a kitchen drawer gets blunted by everything it rattles against, and sheaths get lost within a year. DMT’s handles “enclose and protect the diamond serrated sharpener when not in use,” which turns an easily ruined tool into one you can keep next to the whisks. At 5 inches closed it fits anywhere.
It is faster than a stone and slower than you expect.DMT claims it “sharpens knives faster than conventional stones” thanks to the monocrystalline diamond surface, and on a per-stroke basis that is believable — diamond cuts hard steel quickly. But a 9-inch bread knife has thirty-odd gullets and each one needs the same small number of strokes as the last. The honest expectation is a patient few minutes with the radio on, and that is the nature of the job rather than a fault in the tool.
Light hands.The flip side of a fast abrasive on a small contact patch is that pressure does damage quickly. Three or four light passes per gullet, counted, and the same count on every scallop — consistency is what keeps the tooth line even. A heavy hand rounds the points, which is the one kind of damage this tool cannot undo.
The advice on DMT’s own site we would ignore
DMT’s FAQ recommends “sharpening at a 20-degree angle” and adds that “sharpening at the proper angle is not as important as sharpening at a constant angle.” The second half is good advice everywhere. The first half is written for straight Western and outdoor edges and simply does not apply to a serrated blade: there is no angle for you to set. The bevel inside each gullet was ground at the factory, on one side, and your job is to follow it rather than to choose it. If you find yourself thinking about degrees while using this tool, you are about to put a second bevel somewhere that should not have one.
The same FAQ page carries a warning worth repeating because it applies to every DMT grade: “unless the stone is designated Dia-Flat, do not use for lapping.” This is not a stone-flattening tool. Our flattening guide covers what is.
Who should buy something else
If you will not do it by hand.The Chef’sChoice 15XV is the one electric sharpener we list whose maker documents a serrated procedure — its own manual says to “use only Stage 3” with “five (5) to ten (10) pairs of alternating pulls.” That is maintenance of existing teeth, not restoration of lost ones, and it is the honest trade for not doing the work yourself.
If the knife is not worth the evening. A stamped supermarket bread knife costs less than an hour of your time, and if a pull-through sharpener has already ground its points flat there is nothing to recover. Buy a new knife and keep this tool for the serrated blade in a set you actually like.
If your drawer is all straight edges. Then this is the wrong purchase entirely and a 1000/6000 combination stone from our whetstone roundup is the right one. A tapered cone is a specialist tool for a specialist edge, and its value is entirely in being the only thing that fits.
The verdict
This is the rare case where there is no real competition on capability, only on disclosure and price. The Lansky folding rod does the same thing for less and publishes no abrasive grade; the electric machines mostly stay silent about serrated edges, and that silence should be read as a no. DMT prints the taper, the length, the micron and the mesh, puts the grade on a published table with the rest of its range, and tells you which parts are made where. For a tool that will sit in a drawer for years between uses and then be asked to rescue a good bread knife, that is exactly the set of things we want to know before buying.
