Genuine Hitachi O‑ring (B), part number 998427 — a direct replacement sealing ring used in the valve/cylinder area of Hitachi hammer drills. It’s a flexible rubber O‑ring made to the original Hitachi specification to stop air and oil leaks, so you’ll restore proper hammer action and air-tight performance when you fit it. If your tool has a cracked, flattened or hardened O‑ring, swapping in this part is a quick way to get reliable operation back without extra work.

Fits commonly on Hitachi models such as H65SB2, H65SD2 and related H65SB/H65SD and H70SA series hammer drills.

This piece is straightforward to install: remove the worn ring from its groove, clean the seating area, then press the new 998427 O‑ring into place — no special tools required for most repairs. If you’re replacing a sealing ring to stop leaks and restore full function, this original Hitachi part is the correct choice among Hitachi parts.