This is a slip collar that can be placed on a Chevy Magneto or Distributor base after the original collar has been machined off. The slip collar allows the magneto or distributor to be moved vertically up and down in the engine so that proper cam gear mesh can be achieved in situations such as the block being decked, or tall deck applications.

Note: Once the correct height is determined tighten the large allen screw followed by the two small allen head set screws.