Genuine DeWalt O‑Ring — part number 323711-46. Durable elastomer sealing ring sized 55 × 2.5 mm (55 mm diameter, 2.5 mm cross‑section) designed to restore a leak‑free seal in DeWalt demolition‑hammer assemblies. It’s the small cylinder/housing seal commonly replaced when a tool develops air or oil leaks or loses impact performance. Fits DeWalt demolition hammer models such as D25940K, D25941K and D25951K (sold individually).