A lens stamped Z87+ U6 under ANSI/ISEA Z87.1-2025 blocks 99.9% of ultraviolet radiation in the 200–380 nm band, while a lens marked 2-1.2 or 2C-1.2 under EN 170 is graded on a different scale, where the 1.2 figure is luminous transmittance, not UV attenuation [S1][S5].
Buyers in the U.S. and EU are dealing with two completely different optical-grade languages on the same product. The U.S. ANSI/ISEA Z87.1-2025 system, published January 2026, sorts UV protection into scale U2 through U6, with each step tightening the cutoff. The European EN 170, now folded into EN ISO 16321-1, encodes protection levels with a code-number pair that confuses anyone trained on ANSI markings [S1][S3].
What "U6" actually means under Z87.1-2025
ANSI/ISEA Z87.1-2025 lists U-scale markings from U2 to U6, with U6 being the highest UV-blocking category, meaning the lens blocks 99.9% of UVB and UVA radiation [S1][S3]. The U-scale runs in tandem with other filter scales: R for infrared, L for visible light, and W for welding shade numbers [S1]. A typical full mark set reads "Z87+ U6 L3" for a high-impact, high-UV, glare-reducing lens [S1][S5].
For dust environments, Z87.1-2025 also retains D3 (splash/droplet), D4 (dust), and D5 (fine dust below 5 microns) markings, all stamped on the frame and lens along with the UV code [S3][S4]. The standard requires both the frame and the lens to carry the permanent Z87 mark, with no glue-on labels accepted as compliant [S3].
How EN 170 encodes the same hazard
EN 170, the European personal eye protection standard for ultraviolet filters, uses a different code structure, where 2 means UV protection, 2C means UV protection with good color recognition, and the number after the dash is the luminous transmittance grade (1.2 for very clear, up to 3.0 for darker lenses) [S5]. So a European lens marked 2-1.2 transmits roughly 74.4% to 99.9% of visible light and blocks nearly all UV, while 2C-1.2 adds the color-recognition variant for jobs that need accurate signal-light reading [S5].
EN 170 was integrated into EN ISO 16321-1, the unified international standard, but the 2 / 2C / 3 / 5 / 6 / 9 code format is still the language printed on European-market safety eyewear [S4][S5]. The ANSI U-scale and the EN 170 scale do not map one-to-one: U6 (99.9% UV blocked) is functionally close to EN 170 code 2 or 2C, but you cannot read one stamp and infer the other [S1][S5].
Decision matrix: choosing the right stamp for the job
When specifying safety eyewear, the key is the destination market and the hazard, not which stamp is "better". The following comparison lays out the four most common scenarios spec writers hit, drawn from Z87.1-2025 and EN 170 markings [S1][S3][S5].
For U.S. welding: pick Z87+ plus a W shade number (W1.3 for light work, up to W14 for heavy arc), and add U6 if UV from the arc is a concern [S3]. For U.S. grinding or machining, Z87+ D3 D5 U6 is the conservative pick: high-velocity impact, splash, fine dust, and full UV coverage [S1][S4]. For EU chemical-handling under EN 170, look for EN 166 mechanical grade plus EN 170 code 2C-1.2 or 2-1.2 for UV blocking with color recognition [S5]. For transatlantic shipments, the practical answer is dual marking to both EN ISO 16321 and Z87.1, since neither system is auto-accepted by the other regulator's framework [S1][S4]. For a complete filter-frame mechanical reference, see the industrial filter element overview, since EU frame tests for splash and impact run through EN 166 just like ANSI mechanical tests through Z87.1.
Mechanical and dust markings, and why they sit next to the UV code
Z87+ requires the lens to stop a quarter-inch steel ball at 150 ft/s without cracking or popping from the frame, a test any reputable U6-marked lens passes alongside the UV filter grade [S3][S4]. D3 indicates a tight-seal design for splash and droplet; D4 covers large airborne particles; D5 covers particles smaller than 5 microns [S3][S4]. A U6 lens without D3-D5 is impact-rated for UV but not certified for liquid or dust ingress, which is a common confusion when the only stamp visible is the UV code.
For context on particulate sizing in adjacent filtration, the precision filter reference walks through how 5-micron and sub-5-micron retention ratings are defined in industrial process filtration; the same 5-micron threshold shows up in Z87.1 D5 fine-dust marking [S3][S4]. The "H" suffix in Z87.1 denotes smaller head sizing, "V" denotes photochromic, "S" denotes special tint, and "X" is the optional anti-fog mark tested under DIN EN 168 for at least 8 seconds of fog-free performance in a controlled humidity chamber [S3][S4].
OSHA acceptance and the 2025 edition gap
OSHA's 29 CFR 1910.133 currently incorporates the Z87.1-2010 and earlier editions, while the market has moved to Z87.1-2025, published January 2026, as the latest edition [S3]. This means a Z87+ U6 lens marked to the 2025 edition is still OSHA-acceptable in practice because the mechanical tests are backward-compatible, but procurement specs should reference the 2025 edition to pick up the updated anti-fog "X" marking and the relaxed optics requirements [S3][S4].
European equivalents face a parallel transition: EN 170 is being superseded by EN ISO 16321-1, with the code-2 / 2C filter definitions carried forward but renumbered under the new ISO umbrella [S4]. For buyer-side filter and dust-load math, the bag filter reference gives the same kind of grade-by-grade comparison the Z87.1 D3/D4/D5 table provides, since both systems rely on stated particle-class thresholds rather than efficiency percentages alone.
Specifying U6 / 2-1.2 for a real procurement
A practical specification for a transatlantic site reads: "Safety glasses, Z87+ U6 L3 (ANSI/ISEA Z87.1-2025) and EN 170 2C-1.2 (or EN ISO 16321 equivalent), D3 splash rated, anti-fog per DIN EN 168, with permanent frame and lens marking, no adhesive labels" [S1][S3][S4]. The mechanical grade (Z87+ vs EN 166 grade F or B) and the splash/dust grade (D3 / D4 / D5 vs EN 166 "3" / "4" / "5") are spelled out so the supplier cannot substitute a basic-impact or non-splash lens.
Buyers should also request the test certificate showing the UV transmittance curve, not just the code stamp, because a U6-marked lens and a U2-marked lens both look like "UV protection" without that trace [S1][S5]. For complementary reference material on rad-hard spec drafting and mechanical grade selection on industrial hardware, see the harmonic filter entry, which walks through grade-coding logic on a different but analogous regulatory layer.
Trackable signals for the next six months: confirmation of OSHA's formal incorporation date for Z87.1-2025, expected CENELEC withdrawal dates for pure EN 170 references, and whether the next edition harmonizes the U-scale numbers with the EN 16321 code numbers. Buyers should also watch for EU guidance on cross-acceptance of Z87+ U6-only markings in chemical-handling environments, where EN 170 code 2-1.2 is currently the default. The recent 600 W vs 1100 W percussion drill spec breakdown shows the same code-by-code procurement pattern applied to power tools, and the ANSI B11.0 vs NFPA 79 emergency-stop spec is a good parallel for navigating two regulators that do not auto-recognize each other's stamps.