1074-Machining Center Adjustable Heavy Duty Large Bore Fine Adjustment Fine Boring Bars 200-1200 Bridge Type BST Boring Bars BT50Large Bore Heavy Duty Fine Boring Heads Boring range 200 1200mm 1. The whole system is made of 7075 aviation aluminum, high hardness, light weight, good shock resistance. Multiple locking design is easy to adjust the steel, built in threaded bushings, strong locking force and durability. 2. Micro adjustable dial scale is clear, easy to adjust, divided into 100 equal parts of the circumference of each move a frame for the middle 0. 01mm operation is