Belgard 167000250 6" x 4" x 16" Standard Block Gray - Concrete wall blocks are unsurpassed in functioning as a barrier to contain the spread of fire. These blocks effectively resist transmission of intense heat through the wall while also preventing the passage of flames and hot gases. They are most commonly used for building walls and structures. Their sturdy, heavy composition and stackable design also make them usable in many DIY projects around the house.