Genuine Bosch O‑ring — part no. 1610210209 (also shown as 1 610 210 209). This small sealing ring is listed in Bosch exploded diagrams as item 321/60 and is used as the internal seal on the rotary‑hammer/piston shaft assembly to keep the percussion chamber sealed and preserve hammering performance.

Key specifics you’ll want to know: size/format is shown as an O‑ring roughly 9.5 × 3.5 mm in Bosch power tool parts listings (sold individually), so it’s the correct replacement when that exact ring is worn, torn or missing.

Example Bosch models this part is documented to fit: GBH 2‑28 (and GBH 2‑28 F/GBH 2‑28 DV variants), GBH 3‑28 (including GBH 3‑28 DFR/DRE variants) and the GBH 36 V‑Li / GBH 36 V‑Li Plus family — referenced in multiple Bosch spare‑parts listings and diagrams.

Why this part matters: a worn or damaged O‑ring here allows loss of pressure or grease into the mechanism, which reduces percussion force and accelerates internal wear — replacing it restores the original sealing surface and helps the tool regain correct hammer action.

What you’ll receive: the single genuine Bosch O‑ring, part number 1610210209, ready to drop into the location shown on the GBH exploded diagram (item 321/60).