Marshalltown 8 Stainless Steel Taping Knife. A taping knife is a drywall tool with a wide blade for spreading joint compound. It can be used to spread mud over the nail and screw indents in new drywall applications and is also used when using paper or fiberglass drywall tape to cover seams. Taping knives are an indispensable part of every drywall professional's toolkit."