In this schematic the "Bolt, Small Flange" is used most often.
Parts such as the Water Pump: Oil Seal (12x22x5-371), Bolt, Small Flange, Gasket 256113960000 (nas), Pin,dowel (603) are included in the Yz250f 2004 5xc2 Sweden 1c5xc-100e1 Water Pump parts fiche.
The Water Pump is made up of components including this Cover, Housing which is the most expensive.
