What Is GEOMET? 321, 360, 430, 500 and 720 Explained

Summary: GEOMET is NOF Metal Coatings’ chromium-free zinc-flake coating family. The main products differ in curing temperature, color, lubrication and intended use. This guide compares GEOMET 321, 321 LT, 360, 430, 500, 720 and 720 HP.

The short answer

GEOMET® is NOF Metal Coatings’ family of waterborne, chromium-free zinc-flake coating technologies.^{[1] [11]} Finished parts are coated by applicators in NOF’s licensed network.^[3] The coatings are applied non-electrolytically and then cured with heat. This makes them useful on high-strength steel fasteners, where the coating process must avoid introducing hydrogen.^[2]

GEOMET 321, 360, 430, 500 and 720 are NOF product names. The number is not a salt-spray result: GEOMET 720, for example, is not simply a “720-hour coating.”

For threaded fasteners, the topcoat or lubricant sets the friction that controls clamp load during tightening. It can also change color and chemical resistance.

Where GEOMET fits

Zinc-flake coating is the technology. GEOMET is NOF’s proprietary coating family within that category. A genuine GEOMET system uses an NOF coating product applied by an NOF-licensed applicator.^[3]

Other manufacturers sell zinc-flake systems under their own names. For the broader difference between zinc-flake coatings, DACROMET and electroplated zinc, see Dacromet and Zinc-Flake Coatings for High-Strength Fasteners.

How GEOMET protects steel

GEOMET contains zinc and aluminum flakes held in a binder. The overlapping flakes slow the movement of water and salt toward the steel. Zinc also corrodes in preference to the steel, providing sacrificial protection.^{[1] [11]}

GEOMET uses non-electrolytic deposition, so the deposition stage adds no hydrogen. Acid pickling can still introduce hydrogen before coating, so high-strength parts need a controlled cleaning process.^[2]

Basecoat, topcoat and friction

A GEOMET basecoat provides the main corrosion protection. A topcoat can then add:

coefficient of friction;
black or identification color;
chemical and fluid resistance;
resistance to handling or assembly damage;
more consistent friction after handling or repeated tightening.^[11]

This matters because most tightening torque is consumed by friction. Two bolts with the same steel grade and GEOMET basecoat can produce different clamp loads when their topcoats or lubricants differ.

GEOMET 500 includes lubricant in the basecoat. NOF publishes a coefficient-of-friction range of 0.12–0.18 under ISO 16047, so it can be specified without a separate lubricated topcoat when that friction range suits the joint.^[4]

GEOMET series comparison

The table below uses NOF’s published product data. Final performance depends on the complete coating build, part geometry and application process.

Product	What makes it different	Published data	Typical use or reason to specify
GEOMET 321	General-purpose metallic-silver basecoat	6–15 μm; 720–2,000 h neutral salt spray^[1]	General fasteners and metal parts
GEOMET 321 LT	Lower curing temperature	220–250°C cure; 6–15 μm; 720–2,000 h neutral salt spray^[5]	Parts or production lines that need a lower cure temperature
GEOMET 360	Formulated for brake discs and drums	5–20 μm; 250–720 h neutral salt spray; spray applied^[6]	Brake components exposed to heat and automotive fluids
GEOMET 430	Black basecoat	6–15 μm; 720–2,000 h neutral salt spray^[7]	Parts that require a black zinc-flake basecoat
GEOMET 500	Lubricant built into the basecoat	6–15 μm; 720–2,000 h neutral salt spray; coefficient of friction 0.12–0.18 under ISO 16047^[4]	Threaded fasteners requiring controlled friction without a separate lubricated topcoat
GEOMET 720	Metallic-silver basecoat; NOF publishes the same main thickness and salt-spray ranges as 321	6–15 μm; 720–2,000 h neutral salt spray^[8]	Drawings or OEM specifications that name GEOMET 720
GEOMET 720 HP	Higher minimum published corrosion performance within the 720 family	6–15 μm; 1,000–2,000 h neutral salt spray; normally applied as two coats and two bakes^[9]	Specifications that call for the HP system

“LT” means lower curing temperature, not lower service temperature. GEOMET 360 is also easy to misread: its salt-spray range is lower than those of several fastener coatings because it was developed for brake components, where heat and fluid resistance drive the selection.

Specify thickness, coat count and salt-spray performance as a matched system based on the product data sheet or customer specification.

GEOMET 321 versus GEOMET 720

GEOMET 720 is not inherently better than GEOMET 321. NOF publishes the same main figures for both products: metallic-silver color, 6–15 μm thickness, 720–2,000 hours of neutral salt spray and the same listed application methods.^{[1] [8]}

They are separate formulations used under different specifications and approvals. When a drawing names 321 or 720, quote that product and its complete coating build. A substitution needs approval from the drawing owner.

Salt-spray hours also need context. ISO 9227 defines an accelerated corrosion test; it does not convert test hours into years of service.^[10] For a fastener, friction, thread fit, pretreatment, chemical exposure and the acceptance point for red rust can matter as much as the headline test duration.

What to put on the RFQ

For a GEOMET-coated fastener, state:

exact GEOMET basecoat series;
topcoat or integral lubricant;
color;
coating thickness or mass and number of coats;
corrosion test method, duration and acceptance criterion;
coefficient-of-friction or torque/clamp-force range;
pretreatment restrictions for high-strength steel;
post-coating thread and recess requirements;
approved applicator requirement;
certificate and test-report requirements;
whether substitution requires written approval.

If the proposed finish is described instead as “environment-friendly Dacromet” or a domestic chromium-free zinc-flake coating, see Chromium-Free Dacromet: Standards, Alternatives and Selection.

Catalog note: the products below currently use Dacromet finishes. Request the required GEOMET product by name on the RFQ.