Abstract: Apparatus for translating rotary to linear motion using cylindrical means in the form of a shaft or cylinder with helical grooves, usually having a thread profile.For obtaining good efficiency and large gear ratio, i.e. small linear movement per revolution, the apparatus has been made up from an outer cylinder (1) with a rear transverse portion (5) and a forward outer opening (3) through which an inner cylinder (11) is unrotatably displaceable.The inner cylinder (11) has on its inside a helix groove (12) or thread, in which at least one profiled roller (30, 32, 40) with circular ridges (33) engages. The roller or rollers are eccentrically disposed at one end of a drive shaft (23), rotatably but axially undisplaceably mounted (8) in the outer cylinder (1) at its other end. When the shaft (23) rotates, the rollers (31, 32, 40) roll or follow in the grooves (12) of the inner cylinder (11) and displace the inner cylinder in the outer cylinder.