One such important part is the Assorted Metal Steel Core Plug. While it might appear like a tiny, relatively straightforward component, steel core plugs are crucial for numerous applications in automobile, mechanical, and production markets. What Are Steel Core Plugs? Steel core plugs, sometimes referred to as growth plugs or freeze plugs, are cylindrical parts generally made from steel, developed to load holes or flows in mechanical systems. These plugs are often made use of to seal areas within an engine or equipment, protecting against liquid leakage or the access of foreign contaminants.