Bolt; Hexagonal, etc., which connects the parts detachably using a nut, the tightening torque is usually applied to the nut. It is a flat-ended cylindrical fastening element with a head and threaded body. It is frequently used in robotic projects. It is a product used with a special zinc coating to increase its durability. The dimensions of the products are defined as Diameter - Length in mm. The first measure represents the diameter of the product, the second measure the length. In other words, it is a metric 4 size (4mm thick), 20mm long Phillips head screw.
Flat-ended fasteners suitable for disassembly and assembly are called “bolts”; Other pointed fasteners are called "screws" in general.