Printable trapezoidal nuts for Prusa i3 MK2

Prusa i3 MK2 uses trapezoidal lead screw Tr8x8 (4 threads) on Z axis with black nylon nuts.
These are spare nuts. Tr8x8 is for original lead screw, Tr8x4 (2 threads) is for JKM 42 linear stepper with lead screw http://www.banggood.com/JKM-42-Linear-Stepper-Motor-Trapezoidal-Screw-320MM-0_32NM-p-933434.html

See also http://www.thingiverse.com/thing:1916538