You have to consider the speed at which the shaft will be moving, the housing bore, and the runout. These are important to make sure that you choose an oil seal that will not be exposed to unconducive abrasions.
The ignition spark plug is essentially a small device that is screwed into the cylinder head of the engine. It consists of a central electrode, an insulator, and a ground electrode. When the engine's piston compresses the air-fuel mixture in the cylinder, the spark plug creates a spark that ignites the mixture, causing combustion to occur.


What are Oil Seals and the different types?
Fit the gasket to the cover, making sure any screw holes line up. If the gasket has tongues, fit them into their cutouts.
1. Sealing Element
Refit the rocker or cam cover, aligning its fixing holes with those on the head. Check that the gasket edge aligns with the cover flange all round, and is not distorted. If necessary, adjust it gently with tweezers or long-nosed pliers. Tighten bolts evenly to just compress the gasket.