Features: Sturdy Material:The thread chaser set metric and standard made of Bearing Steel and 40Cr Mold Steel,is strong and sturdy enough to ensure durability for long lifespan. Must-Have Tools:This 49Pcs thread chaser set is a must-have multifunctional tool for automotive mechanics,which can help to clean and restore worn,damaged,rusted threads effectively on cylinder heads,engine blocks,and other body parts. No need to spend a fortune buying new ones. .