Laser cut parts made by MDF 4 or 4.5 mm, but the setting of laser cutting may depend on the machine brand and type. The dark blue circle should be carved a hole into the surface about 1mm, and shallow blue circle is 2 mm deep.
Thumb
This redesigned thumb has less parts and spring free, and original spring is instead by a MDF cut spring.
Plam side
Palm side: its function is fixing the arm bone (included in the finger's AI file). It should to be integrated into the palm part, I will update soon.
Arm skin
I made the arm skin by MDF in previous version, but PP paper has better flexibility and durability. You can get the PP paper (0.75mm) in the Daiso store around Japan.