The eeWings arms are Grade 9 Ti-3AI-2.5V titanium because this particular ti alloy is best for making drawn and formed tubes. The hirth joint/chain ring interface, spindle, pedal inserts, and preloader screw are Grade 5 Ti-6AI-4V titanium, as this alloy is better for machined parts. The main fixing bolt is 17-4 stainless steel. The required 1.75mm spindle spacer, and preload assembly (thread ring and spacer ring) are made of 7075 aluminum.