Parts such as the Crankcase Cover 1: Pin,dowel, O-ring (341), Bolt, Small Flange, Washer (566) are included in the Wr250f 2001 5ph2 Sweden 115ph-100e3 Crankcase Cover 1 parts fiche.
On this parts fiche the Bolt, Small Flange is the most specified component.
The most reasonably priced component used on the Wr250f 2001 5ph2 Sweden 115ph-100e3 Crankcase Cover 1 is the O-ring (2h9).