I've been unhappy with how long and difficult it was to blend fruit in our Oster blender, and decided to make a tamper rod out of a piece of 1.25" poplar rod. Of course, it's crucial for reasons of safety to make sure the rod doesn't touch the blades, so I designed and printed this collar to keep the rod in place and also keep spatter from coming up out of the hole the rod fits in. The collar keeps in place with a screw.

USE AT YOUR OWN RISK!

Of course, you can buy a plastic tamper rod on Amazon, or print a whole rod. However, then you'll be eating more microplastics, since I expect a lot of microplastics will be produced as frozen fruit bounces against the rod.