GB/T 3098.20-2004 in English

《GB/T 3098.20-2004紧固件机械性能 蝶形螺母 保证扭矩》由TC85（全国紧固件标准化技术委员会）归口，主管部门为中国机械工业联合会。
本部分规定了适用于国家标准蝶形螺母的保证扭矩等级、保证扭矩值及试验方法。

1 Scope

This part specifies proof torque class, proof torque value and test method of wing nut applicable to national standard.

2 Proof Torque Class and Proof Torque Value

The proof torque class of wing nut is composed of a Roman numeral, which is only a code not expresses class difference. It's applicable to wing nut specified by national standard.

The proof torque of wing nut shall be in accordance with those specified in Table 1. Where test is conducted under normal temperature according to the method specified in Chapter 4, the thread of wing nut shall be free from thread-off or fracture and the wing part shall also be free from obvious deformation; after removing torque, nut shall be capable of being screwed out by hands or it shall be loosened by wrench but shall not exceed half thread. During test, if bolt is damaged, the test is invalid.

Foreword i
1 Scope
2 Proof Torque Class and Proof Torque Value
3 Test Methods