Pinion lock ring tool

I needed to replace the front sprocket on my stromer ST3, but I didn't realize I needed a special tool to do that. instead of spending 40 euros and waiting for shipping, I designed and printed this in under 40minutes, and it worked from the first time!

• I used 7 bottom, top and wall layers, plenty strong.
• You will need 8 M3x10mm bolts. 
• I drilled out the holes with a 2.5mm drill bit
• Fits a 30mm socket

Too loosen the ring, you need to turn it in a clockwise motion. The sprocket wants to keep turning, so I put a hex key in one of the holes of the sprocket so it could resist the motion when applying force (see picture)