Usually the top two rings in the piston, they form a seal between the piston and cylinder wall to compress the air fuel mixture in the cylinder.
Constant velocity joint
A system that provides fresh air to the exhaust system under controlled conditions to reduce emissions. The air source can be a pulse-air pump or an electrical or belt driven pump. Upstream air injection goes into the exhaust manifold to assist in after burning HC laden exhaust gases. Downstream air injection goes into the oxidation bed of the catalytic converter to help oxidize HC and CO emissions.
A plug used to fill holes in a block or head left from the casting process. Also called freeze, welsh or expansion plugs.