What are the different applications that benefit from the FSW head with retractable pin?

Compared to a conventional FSW head, the FSW head with retractable pin has an additional function: the progressive removal of the pin in the shoulder in order to fill the exit hole of the FSW weld.
As the only FSW tool technology that does not leave a hole at the end of the weld, it is very popular for certain applications, such as space and aerospace applications (tanks, rivet replacement etc.). The exit hole on a cylindrical part becomes a major leakage defect. The retractable pin is particularly used for circular welds (e.g. tanks) in the aerospace industry in order to ensure the tightness of the weld.
The FSW head with retractable pin also offers the possibility of joining parts with a variable penetration depth.