Extends Y axis of  Ender 3 Pro by 30 mm. I am using this on my  Ender 3 Pro after I've installed Y axis damper and a heat sink on the motor. This mod also requires changing the y-axis belt to make it longer. The belt is 6 mm width GT2 timing belt and costs about $7 on amazon for 5 meters. I've removed the brass stops from the original belt and put it on the new one.
Use three 40 mm M5 bolts to fasten the extender.
This mod also assumes that the press-fit pulley on the stepper motor is removed and replaced.

Once hooked to belt - its not going anywhere :-)
Due to small size - better to print with smaller nozzle, like 0.2.
I had none so printed with 0.4 and later had to do small clean up but it still came out well.
Hope it helps
P.S. belt end must be cut at the beginning of the 2mm curve with no flat part before.