a spin or friction welding apparatus which can accurately locate a container such as a semirigid plastic bottle with respect to an overcap which is to be frictionally welded to the bottle by means of a rotatable spindle member . in order to assure that the overcap is secured to the bottle neck when employing high production machinery utilizing a rotating spindle mechanism for frictionally engaging the cap on a stationary bottle , many tolerances must be compensated for in the dimensions of the cap , the size of the neck on the container , as well as the positioning of the cap in relation to the container . to compensate for these variables , a biasing means is provided in conjunction with the rotatable spindle member so as to effect a predetermined tension on the cap member when it engages the stationary container neck and is spun into frictional engagement with it . further , means are provided in the form of oppositely disposed jaw members with surfaces to surround the neck of the container and position it precisely in axial alignment with the rotatable member . to further assure proper alignment during frictional engagement of the cap and the container neck , the support means for the container is moved out of position so that the only vertical support of the bottle is by means of these jaw members which contact the lower surface of the rib on the container neck . this support contact prevents vertical deformation and horizontal deflection of the bottle and rotation of the bottle is prevented by means of lateral wall members .