My daughter is developmentally disabled and on the Autism spectrum. I also have the privilege of working with a number of students across my school district that have Autism and other sensory needs. This fidget is the first of a few designs we made for our students with specials needs. It uses a standard skate bearing (8mm x 22mm x 7mm) in the middle. Each of the sides has a different texture that students can feel. Many of our students (including my daughter) enjoy rolling the fidget on their arms and hands.
If you have any other ideas or suggestions, please let me know in the comments below.