I'm working on a project using Bourns rotary encoders (PEC12R-4015F-S0024), and I modeled up a cap for them. My model should work on any Bourns encoders with a diameter of 6mm (mine all measured at 5.9mm), and any others that share dimensions. The hole is 5mm deep to the bottom of the chamfered edge inside (to print without supports).

That being said, I'm providing the Fusion file to modify as you please!