After confirmation from the course teacher, we broke the original palm zester to extract the metal zester part.

Smoothened the edges of the fingers slots for an easier grip.  

After observation of the zester, I've found small holes on each side of the grater, so I decided to add small hooks on the inside of the device to wedge in the zester, which will afterwards be secured by a set of rings with a clearance gap of around 0.05 mm.