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The Authoritative Guide to #4 Finishes

In the metals polishing industry, the #4 (N4) Finish is the most common architectural or industrial finish regardless of the end-use application. Although it is a routine and less labor intensive finish, the #4 finish is a highly technical finish with a variety of distinct permutations. The #4 finish often escapes concrete definition due to the varieties available and the ambiguous nomenclature surrounding this surface finish. At Diamond Brite Metals, the majority of requested finishes is the #4 finish. Our wide coverage of end-use applications and vast experience in the metals polishing industry has allowed us to fully define the #4 finish. We routinely produce all industry standards of the #4 finish including the surface variations that comport with ASTM, ASME, ISO, and AISI definitions. Each definition has two parts: grain pattern and the finish.

#4 Grain Patterns

Short-Grain (also known as the “brushed finish/brush #4” or “satin #4): the grain pattern is comprised of short-intermittent grit lines caused by the polishing or abrading by an abrasive belt. The short-grain is more prevalent in industrial end-uses where there is less of a demand for aesthetic or ornamental appeal. The short-grain pattern can be applied as a commercial #4, true #4, or sanitary #4.

Long-Grain (also known as the “hairline” finish”): the grain pattern consists of continuous grit lines caused by an extended polishing or abrading by an abrasive belt. The grit lines are not interrupted or intermittent like the short-grain pattern. The long-grain finish is more labor intensive and more difficult to achieve. The long-grain finish is more prevalent in architectural capacities. The long-grain pattern can be applied as a commercial #4, true #4, or sanitary #4.

#4 Finishes

Commercial #4 Finish: The commercial #4 finish is the standard for a wide variety of industrial end-uses. Customers request this finish when project specifications demand a relatively coarse finish but finer than a mill finish. This finish is sufficient for when customers request a low cost finish. Unless otherwise specified, this finish will be the default #4 finish provided by a distributor or polisher. Zirconia abrasive belts ranging from 80 to 120 grit achieve this finish.

True #4 Finish: The true #4 finish is more labor intensive and the surface quality is finer. The finer surface quality increases the aesthetic appearance of the product so true #4 finishes are requested when heightened attention must be paid to aesthetic appeal. Architectural fabricators will often request this fine #4 when quoting highly visible and highly trafficked projects. Zirconia abrasive belts are utilized in successive stages ultimately reaching a 180 grit.

Sanitary #4 Finish: A sanitary #4 finish is the highest quality #4 finish and produced at the end of the #4 finish grit range. The fine surface quality achieved through fine abrasive belts meet regulatory specifications. Customers involved in the pharmaceutical and food and beverage industries, and subject to heightened regulatory requirements from the Food and Drug Administration, frequently request a sanitary #4 finish. This finish ensures that products are free from pitting and diminutive surface flaws. Zirconia abrasive belts ranging from 220-240 grit impart the final pass for this finish.

The #4 finish is the proverbial workhorse in the metals industry. With a wide variety of applications, the #4 finish is suitable for most project’s needs. But, before requesting a #4 finish, a customer must understand the nuances of this surface finish.



Diamond Brite Metals, LLC is a comprehensive architectural and commercial polishing facility located in Middlesex, New Jersey. We welcome any and all inquiries regardless of size or complexity. To submit an RFQ, please contact our Sales Team at For architectural projects, please contact, Colton Karpus at

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