Gaskets are mechanical seals between two objects, usually used to prevent pressure, corrosion, and natural thermal expansion and contraction of pipes between two objects and leakage. Since the machined surface cannot be perfect, the irregularities can be filled with spacers.
Rivets are a type of fastener that connects two materials permanently. While there are several types available to support a variety of applications, they all have three main components: a cylindrical shaft that is inserted into a pre-drilled hole, a fixed head on one end, and a tail that is “bucked” to expand in diameter and fasten it in place using a special tool.