This is a couple of objects that can be printed and used in a tool to restore 3 inch core in rolls of media that have been damaged. The cardboard core will be out of round and may not load in an engineering plan printer or other equipment. This solution allows you to restore the core with one of these 3-d prints and assembled with a 3/8 inch flange, 4 inch long 3/8 nipple, a 3/8 to 1/2 inch female to female union, a 3 foot pipe with male threads on each end and possibly a couple of washers. You want the flange on one side of the 3-d print and the 4 inch pipe through the center of the nipple, then a washer, then the 3/8 to 1/2 inch union, the 1/2 inch pipe threaded on both ends, and finally the cap. See pictures for assembly. Here is a youtube video link showing the assembly of the tool https://youtu.be/4thX6eujX70

how to fix a 3-inch core on a roll of paper: https://youtu.be/YlAGULDSSm0