Self-tapping inserts (also known as self-threading inserts ) have internal and external threads, and are designed to cut their own threads as they are being driven into a drilled hole. The thread cutting action is performed by the cutting slots on the inserts. By tapping its own thread, the self tapping insert eliminates the need for pre-tapped holes.

The use of self-tapping inserts has significant advantages over pre-tapped holes, moulded-in inserts and wire thread inserts. They eliminate close tolerance holes required for tapping directly into the base material, damaged tools and low productivity resulting from moulded-in inserts and the time consuming process of placing wire thread inserts into pre-tapped holes.

The use of a self-tapping insert can result in a reduction in thread size required because of the insert's large effective shear surface saving material and reducing cost and weight.

External Thread Interference

For a work-piece made of a light alloy, this diagram illustrates clearly that whilst correct hole sizes are important for product reliability, the Ensat 302 achieves almost maximum pull-out with only 30% external thread interference.

Pullout Resistance

In light alloy, the self-tapping steel insert resists a pullout force in excess of the yield point of an 8.8 grade bolt.