The expansion of a Lee Plug causes the boss material to be deformed, resulting in radial growth of the boss I.D. and O.D. In order to accommodate this growth, some consideration must be given to the ductility of the boss material. Generally, the boss material should have an elongation of at least 3%.
A typical Lee Plug installation will expand the boss I.D. by approximately 0.003 inch. Since this expansion remains relatively constant for all sizes of plugs, the smallest sizes are subject to the greatest percentage deformation. The worst case is a 0.093 inch diameter plug which will be expanded to 0.096 inch in a boss, or 3%. Thus, if the boss material has an elongation of over 3%, the boss will not crack from installation of the Lee Plug.