What kind of expansion screw is used for shaping guardrail?

Fences generally use 30 square pipes, and holes with a diameter of 8.5 mm are just right. Too much hole will affect the strength of square pipe. The 8 mm expansion screw is generally a hole of 12. No matter how big the hole in the outer wall is, it is not easy to fight.

Generally speaking, the expansion screw is a metal expansion screw, and the fixation of the expansion bolt is to use the wedge-shaped inclined plane to promote expansion to generate friction and grip force, so as to achieve the fixed effect.