Thx Dman! 3d printed protos of the shark fin. So far works like a charm! Soon to be added to the Centri. All previous orders will receive one for free. Makes your rubber band easier to use and is setup to counter act cartridges as well, all in a fin that easily grabs onto the tension pullie. These plastic ones work great so the aluminum should be NICE! Coming soon!!!10313143_729489370430406_4065994273588984054_n.jpg