A coupling is generally a connecting intermediate part that joins two components, commonly used in construction engineering for fixing steel tube scaffolding with an outer diameter of Φ48mm. Couplings are categorized into right-angle couplings (cross couplings and directional couplings), swivel couplings (movable couplings and universal couplings), and butt couplings (straight couplings and direct couplings), among others.