Reading Metal Markings & Stamps for Identification: The Scrap Master's Secret Code
These seemingly small numbers and letters can provide precise information about a metal's type, grade, and alloy, often leading to a higher payout than if you simply guess. This guide will show you how to read these vital clues.
Why Markings Matter: Precision for Profit
While the magnet test is fundamental, it won't tell you the exact grade of stainless steel, or the specific alloy of aluminum. That's where markings come in. Scrap yards often pay premium prices for precisely identified, clean, and segregated alloys. Knowing these codes can prevent your high-value metal from being downgraded to a lower, "mixed" rate.
Common Markings & What They Mean:
1. Copper Piping & Tubing
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ASTM Standards (e.g., ASTM B88, B280): These indicate the standard the pipe meets.
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Pipe Size: Often stamped directly (e.g., "1/2," "3/4," "1").
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Type:
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Type K: Thickest wall, often green print on the pipe. Used for underground lines, heavy-duty applications.
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Type L: Medium wall, often blue print. Most common for interior plumbing.
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Type M: Thinnest wall, often red print. Used for lighter residential applications.
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Type DWV: Drainage, waste, and vent. Thinner than M, not for pressure.
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Manufacturer Stamps: Logos or names of the company that produced the pipe.
2. Stainless Steel
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Series Numbers (Most Crucial): This is the key identification for stainless steel grades.
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304: The most common non-magnetic stainless steel. High value. Often found on sinks, appliances, kitchen equipment.
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316: A higher grade than 304, with added molybdenum for increased corrosion resistance (especially against chlorides). Also non-magnetic, and generally commands a higher price than 304. Found in marine, medical, or chemical applications.
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430: A common magnetic stainless steel. Lower value than 300 series. Found in some kitchenware, appliance trim.
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Where to Find: Often stamped on the edge of sheets, inside appliance doors, on commercial kitchen equipment, or industrial pipes/fittings.
3. Aluminum
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Alloy Numbers: Aluminum is alloyed with various elements, and specific alloys have different values.
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6061: A very common general-purpose alloy, strong, good for welding. Found in structural components, automotive, marine.
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6063: "Architectural alloy," often used for extrusions like window frames, door frames, and railings. It's easily extruded and has a good surface finish.
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3003: Common for general purpose sheet metal, often in cooking utensils, storage tanks.
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Cans: Often have a specific designation like "UBC" (Used Beverage Can), but their value is based on form.
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Where to Find: Stamped on structural pieces, sheets, or castings. Sometimes small tags on window/door frames.
4. Brass
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Copper Alloy Numbers (C-Numbers): Less common for general scrappers to find marked, but industrial brass might have a "C" designation (e.g., C36000 for free-machining brass, C26000 for cartridge brass).
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Pressure Ratings: On valves or fittings, indicating their intended use.
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Manufacturer Stamps: Brands on faucets or fittings.
5. Other Metals
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Lead: Less commonly marked with specific grades, sometimes "Pb" (for lead) might be found. Often identified by properties (weight, softness).
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Die Cast/Pot Metal: May have manufacturer logos or part numbers, but rarely specific alloy markings for the common scrapper. Identified by brittleness and appearance.
Where to Find These Markings:
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Pipes: Along the length of the pipe, often repeated.
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Sheets/Plates: On the edges, corners, or undersides.
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Fittings/Valves: Cast into the metal body.
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Appliances: On internal components, data plates, or on the back of panels.
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Auto Parts: Cast into engine blocks, transmissions, or specific part numbers on smaller components.
Tools for Reading & Researching:
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Good Lighting: Essential for seeing faint stamps.
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Magnifying Glass/Loupe: For tiny or worn markings.
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Wire Brush: To clean away dirt, paint, or light rust revealing the stamp.
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Online Research: If you find an unfamiliar marking (e.g., "AL 6061"), a quick Google search for "[metal type] [marking] scrap value" or "what is [marking] metal" can provide valuable information.
Limitations & The Scrap Master's Caution:
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Not All Marked: Many common scrap items (especially those that have been heavily used or exposed to weather) won't have discernible markings.
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Erosion/Paint: Markings can be worn away, painted over, or rusted beyond recognition.
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Disguised Alloys: Some alloys can be tricky without specialized tools (like an XRF gun, which is not practical for most scrappers).
However, when you do find clear markings, it's a huge advantage. It allows you to confidently sort higher-grade materials, get a more accurate quote from the scrap yard, and significantly boost your payout. It's another layer of expertise that distinguishes a casual collector from a true Scrap Master!
Ready to dive deeper into all types of metal identification and master the art of maximizing your scrap profits?
Explore our comprehensive courses at The Scrap Masters University and learn to spot every valuable detail!