Lifting Sling,Ratchet Strap,Safety Belt Shackles,Hook,Link Chain Co., Ltd. , http://www.goshardware.com When we are working on the upper and lower needle plate slots (Fig. 1), the upper and lower needle plate slots are required to be aligned, and the precision is high. Originally processed on a trampoline, the dial and the dial gauge ensure the groove distance, and the error is large. To this end, we use a longitudinal precision moving device consisting of hanging wheels a, b, c, d. Improved single slot error