Detailed introduction to CL-self tapping helicoil:

Self Tapping Inserts (also known as self threaded inserts) are cylindrical metal bushings with internal and external threads and are specially designed to cut their own threads as they are being driven into a drilled hole. 
 

 CL- Self Tapping Inserts provide permanent wear-resistant threads in a wide range of materials, from tough to tap, high strength steels to brittle plastics.   
 

The thread cutting action is performed by the cutting slots on the CL- Self Tapping Insert. By tapping its own thread, the CL- Self Tapping Insert eliminates the need for pre-tapped holes.