Panetary Gearbox 6:1

6V motor; 200mA; 4200 rpm;
At the output of the gearbox (6: 1) - 700 rpm;

Additionally you need:
2x screw M2x4
1x screw M3x20 ... n
3x screw M3x16
1x nut M3
1x bearing 3x8x4mm

I use thick silicone grease.

z1 = 60;
z2 = 24 (3x);
z3 = 12;

U = 1 + ( (z2*z1) / (z3*z1) ) = 1 + (60 / 12) = 6;