Minimalistic Mk7 replacement - 10mm spring

Changed the "spring-hole" to fit a 10mm OD spring bought from http://reprapworld.com/?products_details&products_id=228&cPath=1595_1666
I also had to increase the height of both parts by 2mm

MK7 Drive gear (first picture) seems to work better than MK8 Drive gear (second picture)