Threaded Inserts Carr Lane heavy duty key inserts are general-purpose threaded inserts with a thick, heavy-duty thread wall, suitable for most applications. Heavy-duty Key Inserts are ideal for thread reinforcement, especially when the mating stud or bolt will be removed frequently. They provide strong, permanent steel threads in almost any parent material – ferrous, non-ferrous, or non-metallic. Heavy-duty Key Inserts are also well suited for quick repair of stripped, damaged, or worn threads. Locking keys positively prevent the insert from rotating.