Screws similar to the three-lobed, but cheaper. They are particularly used on very thin thicknesses. The entrance of the screw allows an easier introduction into the pre-hole, while the carbonitriding treatment gives the hardness necessary for forming the thread and subsequent tightening through the indentation under the head. The product is particularly used in the electromechanical and lighting engineering sector for earthing.
The length of the screw is measured from the tip to the underhead.