Friction stir welding tool insert

A two-piece friction stir welding (FSW) tool insert 100 comprising a pin 104 and shoulder 102 that are manufactured from polycrystalline cubic boron nitride, PCBN. The annular shoulder is a thin disc with a thickness of between 1 and 12 mm and is coaxially mounted about stirring pin 104. Shoulder 102 has a central aperture that is tapered (138, fig. 7) through which the stirring needle protrudes. The shoulder may be unbacked or may have a carbide carrier 110. Shoulder 102 may comprise spiral features on the surface proximate to the stirring pin. Pin 104 may comprise topographical features (spirals and flats) that help induce stirring. Tool insert 100 may be combined with a tool holder (140, fig. 14) to form a tool assembly. The tool holder may comprise a holding member (142, fig. 14), formed from a recessed cup, designed to receive the tool insert.