狼友av永久网站免费极品在线|国产精品亚洲一区二区动漫|国产日产欧美a一级在线|欧美国产私拍在线视频

04.03 2019 Common problems in stainless steel reaming and avoidance methods

When reaming stainless steel, it is often encountered: the surface of the hole is easy to be grooved, the ro

04.03 2019 Three hardness standards for metallic materials

The ability of a metal material to resist the indentation of a hard object is called hardness. According to

04.03 2019 Our fastener industry needs to work hard to improve itself.

Screws are tools that use the physics and mathematical principles of the circular rotation and friction of t