These mechanical linear actuators are preassembled and ready to use. They include an adjustable gearbox that can be positioned at every 90 degrees. The two carriages move toward each other when the handle shaft is turned clockwise. The two carriages move away from each other when the handle shaft is turned counterclockwise. They can be used with simple manual adjustments without complex processes of parts selection, design and assembly. The internal parts are protected from dust by an aluminum profile body and dustproof sheet. The body is made from A6N01 aluminum. End plates made from chrome-plated die cast zinc. The shaft is made from 1045 steel with a black oxide finish. The gearbox is made from 1045 steel, electroless nickel-plated.