CAMI Grit vs FEPA P-Grit: What the Label Actually Establishes

Your coating instructions say P400, but the replacement sheets are advertised as 400 grit. Should you treat them as the same product specification?

Not from those words alone. The P identifies a grading family; an unprefixed number leaves a question unanswered. When comparing CAMI and FEPA P-grit, establish which standard each manufacturer actually claims before deciding that one product can replace the other.

What the letter tells you

FEPA P-grades apply to coated abrasives—the abrasive grains carried on products such as sheets, discs and belts. FEPA distinguishes these from F-grades for bonded abrasives in its standards overview. The P does not stand for “premium,” “polishing” or the paper backing itself.

CAMI is a different grading convention commonly encountered in US abrasive references. It is not simply the name for every grit number printed without a P. A seller may omit a prefix in a short title, use another system, or provide too little information to classify the product.

Nor does buying a sheet in the US establish CAMI grading. Read the package, abrasive backing and technical product information rather than assigning the standard by the seller's location.

Why deleting the P changes the instruction

A grade is a classification of abrasive particles, not a promise that every grain has one exact diameter. Different grading systems do not become interchangeable because a number looks familiar. FEPA itself describes macrogrit diameters as ranges, not single values.

For a coating process that explicitly requires a P-grade, keep that designation intact. Norton's P-graded abrasive explanation shows how the prefix appears in product descriptions and backing imprints, and explains why paint preparation instructions may specify that grading family.

This does not mean that a P-marked product is automatically best for every task. Mineral, backing, attachment and permitted wet or dry use still have to suit the work. It means a named requirement should not quietly become a looser one during shopping.

How to resolve an ambiguous listing

Match the exact product name and part number across the listing, package and manufacturer's data sheet. Ask a specific question: “Which grading standard applies to this product and this grade?” That is more useful than asking whether the paper is “about as fine as P400.”

For example, the description of eQualle's 400-grit, ten-sheet pack identifies 9 × 11-inch silicon-carbide sheets for wet or dry use. Those are useful purchasing facts. The retrieved description does not identify a CAMI or FEPA standard, so the listing alone should not be used to certify a P400 substitution.

If your job simply calls for that known product and its result is already acceptable, retaining the same product identity may be enough for a routine reorder. If a paint system, customer specification or controlled procedure requires P400, obtain the missing confirmation or select a documented product that meets it. A satisfactory-looking trial does not by itself establish compliance with a named standard.

Brief explanation: sandpaper numbers

Once the standard is known, you can investigate whether a cross-system alternative is suitable. Before that, a conversion chart is answering the wrong question: it compares identified grades, while your problem is an unidentified label.

Record the designation in the job file

Once the grade system is confirmed, preserve the evidence with the work instruction: manufacturer, product family, backing code, complete grade, and data-sheet revision. Photographing only the large “400” on a package recreates the same ambiguity for the next order. For production or customer-specified work, require purchasing to substitute only against the complete approved description. A conversion chart can help discuss candidates, but an authorized person still needs to approve the change and the trial or inspection method that proves the process remains acceptable.

A practical receiving check should compare the label on the box, the imprint on several sheets, and the purchase specification before the abrasive reaches the job. Quarantine a shipment when those identifiers disagree. Do not average the markings or assume that mixed packaging is cosmetic. If a manufacturer changes a product code or grading declaration, treat the revision as a process change until the responsible person has reviewed it. This is especially important when the abrasive prepares a coating for adhesion or produces a customer-defined cosmetic scratch pattern. The cost of clarifying one label is usually far lower than reworking a completed surface whose specified P-grade was never actually confirmed.