n1/n2 = Z2/Z1 = D2/D1 = P2/P1 = 2
n1, n2: velosity of screw, nut
Z2, Z1: number of threads of nut, screw
D2, D1: average diameter of nut, screw
P2, P1: pitch of threads of nut, screw
Screw and nut have same helix direction (right-handed) and rotate in the same direction.