This is a remix of BluePlexus's Orbit Sprinkler Knob. His looks and fits perfect, but the connection point to the timer itself was too weak. So, I reinforced the connection point, and then printed it at 60 degree angle. I feel the angle helps with the strength of the part.

On the timer itself you will need to remove the plastic that surrounds white stem. Don't break the stem itself as this will ruin the timer. Just remove the blue (or whatever color your timer is) that surrounds the stem. This allows the reinforced part of the knob to fit onto the timer.