BS 7371-7:2010

• 25.220.40 Metallic coatings
• 21.060.10 Bolts, screws, studs

This part of BS 7371 specifies requirements for coatings applied by mechanically impacting zinc powder, or zinc based powder on to the component surface in an aqueous medium. The coating is not applied by using impact media accelerated by compressed air or centrifuge methods. The coatings consist principally of zinc and can be lubricated to give controlled torque/clamping force properties when required.

NOTE 1 See, for example, BS 7371-2.

In addition to the requirements in this part of BS 7371, the requirements in BS 7371-1 which are applicable to mechanically applied zinc based coatings apply.

This part of BS 7371 also specifies requirements for:

1. the coating thickness;

2. the type of conversion treatment to be applied, which can be hexavalent, tri-valent or chromium free;

3. the quality assessment of the corrosion resistance of unused coated parts when subjected to neutral salt spray testing;

   NOTE 2 See, for example, BS EN ISO 9227.

4. the adhesion test.

The coatings are suitable for application to metal components such as:

1. parallel threaded fasteners and accessories;

2. screws that cut or form their own threads, e.g. self-tapping screws;

   NOTE 3 See, for example, BS 4174.

3. woodscrews;

   NOTE 4 See, for example, BS 1210.

4. springs and spring components;

5. pipe nuts and connectors with parallel or tapered threads;

6. composite fasteners incorporating non-conducting materials (e.g. rubber-bonded assembly).

When these coatings are applied to non-ferrous fasteners, the only part of the specification that applies is the coating thickness requirements.

Annexes include tables indicating suitable coating grades for standard screw threads and methods of determination of coating thickness.