This the core that is inserted in the middle of the tape reel to hold it in place in the dispenser. For 26mm id reels, they are what I think is a standard for office dispensers. Our original reel is often lost, so now we all can print them. It is tapered a little, to help insert the core in the reel. It holds quite firm in the reel.
The author marked this model as their own original creation.