Many types of seals are used for complete engine blocks. The purpose of the seal kits is to ensure that when an engine block needs to be completely disassembled for repair or refurbishment, all used seals can be replaced again. The advantage of these packages is that they contain all the seals for a given block, so there is no need to buy the seals from several different sources, risking that one or the other seal may not be for the given block.