Custom carbon steel hardened thin head zinc plated blue patch screw

Industry knowledge：

What is combination screw?

Combination screws, as the name implies, are the screws and washers used together. It also called sems screws.
It is a combination of a screw and a washer, which are fastened together by threading. There are also many types of head style and washer style. The stability is stronger than the general screws, so it is often used on many occasions.