ATMU vs DCI: Which Is the Better Buy in 2026?

Same yardstick, side by side (as of August 2026). Valuation lined up like this is most meaningful for two names in the same corner of the market, which these are. Figures are approximate; verify before investing.

Reading it: ATMU is the cheaper of the two on forward earnings, but cheaper is not the same as better. Pair the valuation with growth (how far the forward P/E sits below the trailing P/E) and risk (beta) before you decide.

The metrics above tell you which is the marginally better business. The bigger risk for most people is not picking the slightly worse stock, it is over-concentrating. ATMU and DCI share themes, so owning both, or adding either to what you already hold, can quietly push a large share of your portfolio into one bet.

This is the part a generic comparison page cannot answer, because it depends on what you own. Connect your brokerage and Walnut shows your real, combined ATMU and DCI exposure, flags overlap with your existing positions, and tells you if adding one would tip you past a concentration you are comfortable with, read-only by default, with your login staying at your broker. Walnut is not an investment adviser.

Atmus Filtration Technologies designs and manufactures filtration products, principally under the Fleetguard and Nelson brands, for commercial trucks, construction and agricultural equipment, power generation and marine engines. The core products are unglamorous and consumable: fuel filters, lube filters, air filters, crankcase ventilation systems, coolant chemicals and exhaust components that wear out on a schedule and get replaced by a fleet mechanic, a dealer or an independent shop. Cummins carried the business for decades before spinning it out through a May 2023 IPO at $19.50 a share, then disposing of its remaining stake in March 2024. What is left is a roughly $1.8 billion revenue company with about 4,500 employees, a global distribution network reaching hundreds of thousands of service points, and specification positions on engine platforms that were locked in years ago.

Full ATMU guide

Donaldson Company, Inc. (NYSE: DCI) makes filtration systems and, more importantly, the replacement filters that go into them. Three segments carry the business: Mobile Solutions, the largest at roughly ~62% of fiscal 2025 sales, covering air and liquid filters plus emissions systems for off-road machinery, trucks and the independent aftermarket; Industrial Solutions, covering dust collection, compressed air, gas turbine intake and, since May 2026, jet fuel filtration through the acquired Facet business; and Life Sciences, a smaller unit spanning food and beverage process filtration, disk-drive filters and an assembled bioprocessing portfolio built from Solaris, Purilogics, Isolere Bio and Univercells Technologies. Filters are consumable and often regulated, so a machine sold once generates parts revenue for a decade or more.

Full DCI guide

Both fit overlapping themes, but they are not interchangeable. The useful comparison is which set of drivers and risks you want exposure to.

• ATMU drivers: Aftermarket filtration demand; The Koch Filter industrial pivot.
• DCI drivers: Replacement filters as the recurring base; Facet and a heavier aerospace, defense and power tilt.

A faster-growing, richer-valued name usually swings harder, so it suits a longer horizon and a higher tolerance for volatility; a steadier, more cash-generative business suits a more conservative or income-minded investor. The honest test is which set of risks you could hold through a drawdown: The most obvious exposure is cyclical: first-fit volumes track new truck and off-highway equipment builds, and those have been pressured by tariffs, freight softness and uncertainty around 2027 model-year emissions rules. For DCI, mobile Solutions ties a majority of revenue to off-road and on-road equipment cycles, so agriculture, construction and truck build rates set the direction of first-fit volumes regardless of how steady the aftermarket is.

Growth-minded investors who believe the theme has years to run tend to accept the richer multiple for more upside; value-minded investors lean toward the cheaper forward earnings and steadier profile. Pick ATMU if you believe its drivers more; DCI if you believe its. Many investors hold both, but since they share themes, that is a concentrated bet, not diversification. Decide deliberately and check overlap. For the full detail, see the ATMU and DCI guides.

ATMU. First quarter 2026 sales rose 14.6% to $477.5 million with adjusted EPS of $0.69, and full-year guidance calls for $1.945 billion to $2.015 billion of revenue, a 19.5% to 20.5% adjusted EBITDA margin and adjusted EPS of $2.75 to $3.00. At roughly 21 times trailing earnings the stock trades at a modest premium to the broader industrial group, which reflects the recurring aftermarket mix rather than the growth rate. Net debt sits near $789 million, or a little over two times adjusted EBITDA, following the Koch Filter purchase.

DCI. Fiscal 2026 ends July 31, so the April quarter is the most recent reported period and fourth-quarter results are due August 26, 2026. GAAP EPS of ~$1.00 versus ~$0.48 a year earlier overstates the underlying improvement, because the prior-year quarter absorbed a ~$62.0 million impairment; adjusted EPS rose a more ordinary ~7.1% to ~$1.06. Nine-month operating cash flow of ~$293.8 million funded ~$104.0 million of dividends and ~$108.5 million of buybacks before repurchases were paused, with the quarterly dividend at ~$0.32 per share for a yield near ~1.3%.

Headline figures (approximate, August 2026): ATMU shows revenue (ttm) ~$1.83B, net income (ttm) ~$211M, eps (ttm) ~$2.55, market cap ~$4.4B; DCI shows revenue (ttm) ~$3.81B (+4.4% YoY), q3 fy2026 sales (quarter ended apr 30, 2026) ~$995M (+5.8% YoY), a record, adjusted operating margin ~16.6% in Q3 FY2026, an all-time high, fy2026 adjusted eps guidance ~$3.94 to ~$4.01 (7% to 9% growth).

ATMU and DCI are related but distinct: same themes, different businesses and risks. Neither wins in the abstract; the right pick is whichever thesis you actually believe, sized so you are not over-concentrated in one theme. Walnut can show your combined ATMU and DCI exposure against your real portfolio. It is not an investment adviser.