Bicycle spacer ring for a 7sp cassette

I designed a spacer ring to mount a 7 speed cassette on a 8 or 9 speed hub for my bicycle. My bike is a 7x3 speed, but unfortunately you can only get descent 8 speed wheels. To mount a 7 speed Shimano cassette I designed this spacer of 3mm so that the cassette fits.

The ring is a little bigger in the design (3.1mm) to compensate for shrinking. 

Printed it in PLA 100% infill.

Although PLA should be strong enough,  ABS or PETG should also be possible.