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Marking of bolts and nuts

Manufacturer’s mark, property class, material, batch: what is marked on the part and why

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Term explained

Manufacturer’s mark, property class, material, batch: what is marked on the part and why

Marking is a fastener’s identity card. It allows the part to be traced even years later: to the manufacturer, to the property class or material grade, to the batch and therefore to the certificate. For bolts of 8.8 and above and nuts of class 8 and above, ISO 898 requires the manufacturer’s mark and the class; ASTM A193 and A194 require the grade and manufacturer’s mark; codes such as AD 2000 W7, KTA or the classification societies add their own requirements, often including the inspector’s stamp.

Quenched and tempered nut on the heat treater's delivery note

What is marked on an RS Randack part

  • RS: The manufacturer’s mark, shown on the certificate and registered with the inspection bodies.
  • Property class or material grade: 10.9, B7, L7, A4-80 or an abbreviated material number, for example 6580 for 30CrNiMo8 or 7709 for 21CrMoV5-7.
  • Batch number: Links the part to the steel mill’s heat and the mill certificate.
  • Order number or customer marking: Purchase order number, item number, drawing number or a mark specified by the customer.
  • Inspection stamp: The mark of the inspection body after a successful 3.2 inspection.

The marking is defined in the item master data and is part of the works order; it is applied to the head, the end face or, on nuts, the chamfer.

How parts are marked

By stamping with a punch or hydraulically, before coating and deep enough for the characters to remain legible under zinc flake, phosphate or PTFE. The first marking of each lot is checked and signed off by a second employee, followed by sample checks. Companion test bars carry the works order number so that the test results can be clearly assigned to the lot. On request, in-house laser marking, colour coding per batch or tags with barcodes are available.

What you should specify

Requirements from the standard, code or drawing, customer marking, position of the marking, whether the inspector applies a stamp and whether colour coding is required.

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