Genuine Bosch O‑ring — part number 160021005B. A small rubber sealing ring for the fluid/nozzle assembly that stops leaks and restores steady spray performance; a straightforward, genuine Bosch spare from the range of power tool parts.

Compatible with Bosch spray-pistol models such as the PFS 1000 (3 603 B07 000 / 3 603 B07 070), PFS 2000 (3 603 B07 300 / 3 603 B07 370) ; sold as a single replacement O‑ring ready to install in the nozzle / valve groove to stop dripping and return proper pressure.