The Main Circuit Adaptor 86330107 connects the hydraulic pump to the HC25 Hydraulic Rock Drill’s main circuit, regulating oil flow direction and pressure. Generic adaptors have narrow, rough oil channels that cause high flow resistance, reducing efficiency. This OEM adaptor has a large-diameter (≥8mm) oil channel with a polished inner surface (Ra≤0.6μm) to minimize resistance. It is made from high-strength steel (tensile ≥650MPa) to handle 2000psi pressure, ensuring reliable performance until cracking or port wear requires replacement.