969AM8
Cavity Plug
Mack

A cavity plug is used to seal unused openings within engine blocks, manifolds, or housings to prevent contamination by dust, moisture, or leakage paths that could compromise performance. This plug must fit precisely, providing a tight interference or press fit that resists dislodgement during vibration and temperature cycling. By keeping cavities closed, it helps preserve lubrication paths, reduce the ingress of debris, and maintain internal pressure where applicable. Selection depends on material compatibility with surrounding fluids, thermal expansion considerations, and the geometry of the cavity. When installed during maintenance, ensure the plug seats squarely and that any sealing compound or O‑ring is compatible with the service environment. A correctly chosen cavity plug contributes to longer component life and more consistent engine behavior. Source One Parts Center.