... operation 5. rich experience SJ series worm ball screw or screw jack•SJ screw jacks are trapezoidal screw jack, •the trapezoid screw pairs have high precision ... function, it can hold up load without braking device when screw stops traveling. 8. Accessory parts: Motor, hand wheel, ... Metallurgy, construction, irrigation, chemical industry, healthecare and so on. SJ series worm ball screw or screw jack