The O’ring 86473303 seals the interface between the shank stop and housing in HC25 Hydraulic Rock Drills, preventing oil leakage and dust intrusion around the shank stop mechanism. Generic O-rings used here often swell in contact with hydraulic oil within 500-600 hours, losing their sealing ability and causing oil waste. This OEM O’ring is formulated with anti-swelling additives that resist oil-induced deformation, maintaining its shape and sealing performance over 800 hours. Its precise fit (±0.002mm tolerance) with the shank stop’s seal groove ensures a leak-free connection until mandatory replacement.