On this parts fiche the Nut,8mm is the most specified component.
A sample from the products for the Cylinder Head/cylinder include: Valve-assy-reed, Collar, Thermostat, Bolt-flanged-small.
The most reasonably priced component used on the Kdx125-a4 Kdx125sr 1993 Europe Nr Cylinder Head/cylinder is the Bolt-flanged.