Plugs

Metal Detector Test Plugs are high-visibility, certified test standards designed specifically for validating metal detector gravity feed systems. Each plug features a low-density, impact-resistant plastic body with a certified grade 200 precision metal ball visibly enclosed. Available in two sizes — 38mm (1‑1/2") and 51mm (2") — they drop through the detector aperture exactly as product would, delivering repeatable, audit-ready sensitivity confirmation. See also our Test Balls for pipeline, gravity feed, and bagger system validation.

Available in Ferrous Chrome, Non-Ferrous Brass, Stainless Steel (SS304, SS316, SS440), and Aluminum. Two carrier diameters: 38mm and 51mm.

Plug Specifications and Quality Assurance

Available Sizes: 38mm diameter (1‑1/2") and 51mm diameter (2") — select the size matching your detector aperture
Ball Size Range: No fixed maximum — the plug format accommodates any precision ball size required by your validation protocol
Primary Application: Validation of metal detector gravity feed, drop-through, and free-fall inspection systems in food processing and production environments
Contaminant Types: Ferrous Chrome (FE, 7.80g/cc), Non-Ferrous Brass (NF, 8.47g/cc), SS316 (7.95g/cc), SS304 (7.95g/cc), SS440 (7.70g/cc), Aluminum (AL, 2.79g/cc)
Construction: Dual-property carrier — low-density so the plastic is transparent to the detection system, and impact-resistant for repeated use in production environments
Identification: Color-coded by contaminant type; imprinted with ball size, contaminant type, and unique Certificate of Conformance number
Traceability: NIST traceable; documentation available via the CoC Lookup tool on the Test Standard Labs website
Material Compliance: Manufactured from FDA-compliant materials throughout
Ball Standards: Precision balls meet AMBA, AFBMA, and ISO 3290 grade 200 tolerances
Tamper-Proof: Precision ball is permanently sealed inside the carrier — no user-accessible opening

Frequently Asked Questions

Metal Detector Test Plugs — Gravity Feed System Validation

A Metal Detector Test Plug is a high-visibility plastic disk — available in 38mm (1‑1/2") or 51mm (2") diameters — with a certified grade 200 precision metal ball permanently enclosed inside. The plug is dropped through a gravity feed or free-fall metal detector aperture exactly as product would flow in production. If the system correctly triggers a reject signal as the plug passes through the detection zone, the sensitivity check passes. The low-density plastic carrier is transparent to the detection system, so only the enclosed metal ball is detected — accurately simulating a real contaminant of the selected size and material type.

Test Plugs are available in 38mm (1‑1/2") and 51mm (2") diameter. The correct size is determined by the aperture diameter of your gravity feed metal detector. The plug must be small enough to pass freely through the aperture without binding or bridging. Your metal detector manufacturer's validation documentation and sensitivity specification sheet will specify the required test plug size for your system. If in doubt, contact Test Standard Labs — we can help confirm the right size for your detector model.

The precision ball is a certified grade 200 metal sphere permanently sealed inside the plastic plug. It is the actual test contaminant — manufactured to tight tolerances in a specific material (Ferrous Chrome, Non-Ferrous Brass, Stainless Steel, or Aluminum) and a specific diameter that represents the minimum contaminant size your metal detector must reliably detect. Unlike other test formats with a stated maximum ball size, Test Plugs accommodate any precision ball diameter required by your validation protocol, making them exceptionally flexible for gravity feed system validation. Each plug is color-coded and imprinted with its ball size, contaminant type, and a unique CoC number.

Test Plugs are designed specifically for gravity feed, drop-through, and free-fall metal detection systems — the style commonly used in grain, seed, bulk powder, spice, nut, and confectionery processing lines where product falls vertically through the detector aperture rather than traveling on a conveyor belt. For conveyor-belt systems, Test Standard Labs' Standard Test Rods or Fobs are the appropriate choice. For pipeline and pump-fed systems, Pipeline Rods are recommended. For applications requiring a ball-style test piece that rolls through the detector, Test Balls are available in multiple diameters.

The ball diameter should match the minimum detectable contaminant size defined in your HACCP plan, food safety scheme (BRC/SQF/FSSC 22000), or FSMA Preventive Controls program. This threshold is determined by your metal detector manufacturer's sensitivity specification and your product's "product effect" — the degree to which your product masks detection signals. Unlike other test formats, Test Plugs have no defined upper limit on ball size, allowing you to test at the exact sensitivity threshold specified in your food safety plan, no matter how large. For new installations, your detector manufacturer should provide a site-specific sensitivity test protocol.

Test Plugs are available in Ferrous Chrome / FE (52100 steel, 7.80g/cc), Non-Ferrous Brass / NF (8.47g/cc), Stainless Steel SS316 (7.95g/cc), Stainless Steel SS304 (7.95g/cc), Stainless Steel SS440 (7.70g/cc), and Aluminum / AL (2.79g/cc). BRC, SQF, FSSC 22000, and most HACCP-based food safety programs require validation with a minimum of three contaminant types: Ferrous, Non-Ferrous, and Stainless Steel. Stainless steel is the most critical and the most difficult for metal detectors to reliably detect — always test with SS first. Aluminum is often required when your production environment includes aluminum foil, trays, or packaging components.

Yes. Test Standard Labs Test Plugs are manufactured from FDA-compliant materials, are NIST traceable, and include Certificate of Conformance documentation — meeting the traceability and calibration requirements of HACCP-based food safety management systems, BRC Global Standard for Food Safety, SQF Code, FSSC 22000, and the FDA Food Safety Modernization Act (FSMA) Preventive Controls for Human Food rule. The CoC number imprinted on each plug and available via the online CoC Lookup tool provides the documented evidence required during third-party audits and regulatory inspections.

Yes. Every Test Standard Labs Test Plug is imprinted with a unique Certificate of Conformance (CoC) number. Full CoC documentation is available with purchase and can be retrieved at any time using the CoC Lookup tool on the Test Standard Labs website. These certificates confirm ball size, contaminant type, material compliance, and NIST traceability — providing the complete audit trail required for HACCP records, food safety scheme audits, and customer specification verification.

BRC, SQF, FSSC 22000, and HACCP best practice generally require metal detector performance verification at the start of each production run, after any line stoppage or maintenance, at product changeover, and at the end of each shift. High-risk or high-throughput environments may require checks every 30 to 60 minutes. The frequency should be documented in your HACCP plan or food safety program as a Critical Control Point (CCP) monitoring procedure, with each test pass recorded — including the test plug used (by CoC number), ball size, contaminant type, and result.

Yes. Test Standard Labs Test Plugs are universally compatible with all major gravity feed metal detector brands including Mettler-Toledo (Safeline), Fortress Technology, Loma Systems, Anritsu, Cassel, Minebea Intec, and Thermo Scientific. No proprietary adapters or system-specific configurations are required. Simply select the plug diameter (38mm or 51mm) that fits freely through your detector's aperture, then select the contaminant type and ball size specified in your validation protocol.