The thickness of the tube is about 1/8 thick. It slides over the RCBS aluminum primer tube. Just a plain length of steel tube, nothing special that I noted. It looks like a steel shield tube that I got with another press I had. This is where I got the idea.Thanks for the input! A question or 2? Thickness of tube, and type of tube, going over the primer tube. the I.D. isn't a problem. I have used a RCBS priming tool from about when they came out. I never had a problem except getting the primers upside down. I am changing to a high end priming tool.