Hello, I’m designing a plastic coupling sleeve to mount an aluminum shaft (20 mm OD) from the inside. The sleeve needs to grip the shaft firmly enough to transmit rotational torque from a small motor, so there can’t be any slip or independent rotation once assembled.

I’m planning to use flexible radial features (like fingers or tabs) molded into the sleeve to apply internal pressure, but I’m running into challenges balancing enough flex for easy assembly with sufficient stiffness to hold torque reliably. The part will be injection-molded (likely nylon or POM), and there’s limited axial space for long engagement. Has anyone tackled a similar internal gripping design? Curious about feature geometries or section thicknesses that worked well to achieve a secure, non-slip press fit.