Many sizes and shapes of parts can be ultrasonically welded, but it is important to follow a few rules. First, energy transfer from the horn/sonotrode to the joint area, as well as support from the fixture, are critical to obtaining consistent results. Horn/sonotrode contact is ideally in a plane parallel to and as close as possible to the joint, which will also ideally be planar. The parts ideally will have sufficient stiffness and structural integrity that deflection is minimal when the clamp load required to obtain a weld is applied. Delicate details in the immediate area of horn contact, along the energy transfer path, and in the joint area should be minimized so as to avoid destruction by the high-amplitude ultrasound. Horn contact should be on a semi-glossy relatively large surface so as to enhance coupling and minimize marking. Highly stressed areas such as gates should be located away from the horn contact or weld areas. Smooth engagement of the two parts enhances weldability, but any kind of interference fit degrades it.