well ,now I know way you need 12 cm bolts,you have long spacer tube .
Yes ,I tuned my Raket and thanks to DTpropellers ,they been able make one to my own specification.prop. 130cm long and 18inch pich with very nice shape,save me time try to much prop from other machines .
yes its very power full,I dont know how big thrust is (next time I build thrust testing machine)I make video,when my laziness let me,I will share all project.