Forster Small Primer Feed Tube For Co-ax Primer Seater The tube bottoms against the flat surface of the primer housing in the Co-Ax Primer Seater. The bottom of the tube must be funneled in slightly for proper functioning. For several reasons, the tube is made of a light, soft material which may be bent, filed or trimmed with a penknife. The slot in the tube also permits visual inspection to determine if any primers are reversed. Click Here for Co-Ax Primer Seater Instructions