I designed this grip strength trainer to allow adjustable training difficulty. The resistance is controlled by the internal spoke structure inside the ring. By rotating the ring in your hand and thereby changing the spoke density at the point of highes compression, the stiffness of the ring changes as well.
The model effectively provides two main resistance settings: Medium and Hard. However, the final stiffness also depends on the filament you use. A very soft TPU may result in a Soft–to-Medium resistance, while a stiffer TPU may feel more like Medium–to-Hard.
Of course, perceived resistance is somewhat subjective and will vary depending on the user’s grip strength and printing material.

Filament: I used extrudr Flex Semisoft TPU (80A), resulting in a medium strength. The harder the TPU, the harder the ring ;-)
0.2 layer height
enable: avoid crossing perimeters ! This will reduce stringing.
I highly recommend to dry your filament. The design really is prone to stringing
The author marked this model as their own original creation.