These Aeroflow Performance Welsh plug kits are designed for sealing up the casting core holes in your engine block. The expansion plugs help protect against cracks caused by the pressure of frozen coolant and in regular operation will ensure that all vital fluids stay in the engine, where they belong. These complete engine block freeze plug kits include brass Welch plugs and steel oil gallery plugs but do not include cylinder head plugs. Each kit is specifically designed to suit each make and model with all correct sizes included for when you are rebuilding your engine.