Piston rings seal the gap between the piston and the cylinder of the Partner 350 chainsaw: they hold compression and keep oil from getting into the combustion chamber unnecessarily.
Replace them if compression has dropped, there is hard starting, loss of power and bluish smoke. The 38 mm size is given in the name; choose by the piston diameter. Before installing, inspect the cylinder bore: if it is scored, the rings will not last long.
