n1/n2 = Z2/Z1 = D2/D1 = P2/P1 = 2
n1, n2: velosity of screws 1, 2
Z1, Z2: number of threads of screws 1, 2
D1, D2: average diameter of screws 1, 2
P1, P2: pitch of threads of screws 1, 2
Screws have opposite helix direction and rotate in opposite direction.