Sticks into the lifter bore to hold the dial indicator perfectly perpendicular to the camshaft center line. If you have the head on already, you cannot use it.
just bought one of those from Feebay. came out a bit less w/ free shipping there than Summit or Jegs would have been
also got me a barette from a different seller so I can hopefully CC my head for this engine. wish I could have had someone close I could borrow each from, for "this" job....
