What to specify for a zinc-flake coated custom screw

Identify the complete system

State the required coating specification and any topcoat, sealer or lubricant condition. A trade name alone can leave several technical choices unresolved. Make clear which requirements are mandatory and which can be proposed for review during quotation.

Review the base material and pretreatment

Consider the material condition and the complete treatment route, including cleaning and preparation. A non-electrolytic deposition step is not permission to ignore other process risks. Any hydrogen-related requirements should follow the applicable material and coating specification rather than an assumption based on appearance.

Include thread and bearing behavior

Coating can affect the fit and assembly conditions. Identify threads, seating faces and other functional surfaces, and state any friction-related requirements that the joint design uses. A corrosion requirement and a tightening requirement are different acceptance topics and should be documented separately.

Write measurable acceptance requirements

Where corrosion testing is required, specify the agreed method and criterion. Do not translate a test duration directly into a field-life guarantee. Include thickness, appearance, fit and process documentation as appropriate to the actual component and the supplied condition.

Specification example

For a high-strength flange screw, supply the mechanical requirement and the selected surface system together. This lets the supplier review pretreatment, final thread checks and any specified friction condition as one route.

RFQ checklist

• Coating and topcoat specification
• Base-material condition
• Pretreatment requirements
• Thread fit and assembly behavior
• Agreed coating acceptance tests