Plug screws, code EN47R21, are robust closing and securing elements used to seal auxiliary drillings, inspection points, and service channels within the MAN L21/31 engine. Produced from high-strength alloy steel and machined to exact thread tolerances, they ensure pressure-tight closure and reliable mechanical strength even under severe vibration and thermal cycling. Their design allows easy removal for inspection and maintenance while guaranteeing safe re-sealing during reassembly. With corrosion-resistant surface protection and precise seating geometry, plug screws contribute to the integrity of the engine structure, prevent medium leakage, and enable controlled and efficient servicing procedures.