This is a single piece prop balancer, that can fit up to 10" props spinning all the way around. I wanted a one piece design for alignment and accuracy at the expense of portability/storage space. For use with: http://www.amazon.com/gp/product/B001BHK54W/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1 (or any other figertip balancer with the same axle length, approximately 1.92in/48.8mm) Also need 1/4 in magnets, I had these sitting around: http://www.amazon.com/gp/product/B0012AUU84/ref=oh_aui_search_detailpage?ie=UTF8&psc=1Printed with ABS, 10% infill, 3 layer top/bottom/perimeter. After printing, glue the magnets into the slots, I recommend a hot glue stick but any adhesive will do. Finally put the prop balancer on with your prop and spin and balance. Also I recommend sanding the backside of the prop over applying tape. From a materials, structural, and aerodynamic point of view, its a safer bet. You remove an extremely thin layer of material, and can be much more precise than with tape.