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Diamond Brite Metals’ Reference Guide for Surface Finishes

At Diamond Brite Metals, we constantly encounter service centers, fabricators, and mechanical contractors who refuse to quote or become involved with polishing jobs because of the ambiguity surrounding surface finishes. These customers are uncomfortable and hesitant to subcontract polishing for their customers because of the uncertainties involved with this mechanical process and the possibility of miscommunication due to the lack of a standardized, polishing vernacular. While we understand their fear, they are sacrificing margin and ignoring additional revenue streams with their risk adverse selling/purchasing strategy. For service centers, in today’s competitive marketplace for the sale of raw material, competing on price means sacrificing margins. For fabricators, avoiding polishing means “no quoting” or “passing on” jobs that involve polishing. By subcontracting for polishing, service centers can increase margins and fabricators can expand their markets.

As the country's expert on metals polishing, Diamond Brite Metals has sought to resolve the ambiguities surrounding surface finishes through the issuance of numerous guides. Last week, we explained the differences between a product's ultimate finish and the underlying grain pattern. Also, we have delineated the nuanced differences between a commercial #4 finish, a true #4 finish, and a sanitary #4 finish. However, to create a uniform, authoritative language, there needs to be a mode of cross-referencing the different surface finishes. For example, a #4 commercial finish relates to what RA finish? What is the corresponding ASME-BPE finish on the ID of stainless-steel pipe and tube for a 32 RA? To ameliorate this problem, Diamond Brite Metals has constructed a reference chart which defines each industry finish relative to other commonly accepted surface finishes. The remainder of this article will walk you through each comparison to help you better understand surface finishing.

Industry Finish

The “industry finish” is the most common way of referring to surface finishes. Since the definitions are open to interpretation, a potential customer should qualify the precise finish desired prior to placing to an order.

Grit Range

The grit range refers to the coarseness of the abrasive belt used in polishing. Again, the since the definitions are open to interpretation, the customer should qualify the exact finish.

RA Finish

An RA finish is the roughness average of a surface which is calculated through a complex algorithm that measures the distance between the microscopic peaks and valleys on a surface. The RA finish is the most precise measurement because it is certified with a device called a profilometer.

ISO Finish

The ISO finish is a third-party code that defines surface finish. It is rarely used.


The ASME-BPE Finish guide lists the acceptable surface finishes for pipe and tube in bioprocessing and biochemical applications.

Metals polishing can be difficult to understand, but Diamond Brite Metals will aid you through the entire process: from material procurement to installation. We welcome any and all inquiries regardless of size. To submit an RFQ, please contact



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