Abstract: A screw-extruder for shaped food pastes such as spaghetti is removably mounted on a base containing a prime mover. To ensure the safety of the assembly an activator is associated with the cylinder housing the screw and can only actuate a switch in the base when the cylinder is correctly positioned. The actuator may take the form of a manually operable pushbutton on the cylinder, or a lever acted on by the cylinder and acting as a mechanical interlock with a pushbutton and permitting its operation only when predetermined conditions are satisfied. In each case the pushbutton will only act to permit operation of the motor when it is properly positioned relative to a switch in the base.