Apparatus for use in welding a pour spout fitment (22) to a container (32) comprises an ultrasonic welding horn (18) formed with a recess (20) at one end for receiving part of the fitment (22), an anvil (2) between an annular surface portion of which and that one end of the horn (18) are vibratingly pressed a wall off the container (32) and the flange (28) to each other, a head (14) at the opposite end of the head (14) for maintaining an annular, radially inner portion of the flange (28) spaced axially outwards from the annular surface portion of the anvil (2), the outer periphery of the ring (16) being radially dimensioned to be received in the recess (20).