Cast iron square box is mainly used for components parallel, crossed vertical when the test and support the workpiece, usually the same side of the cube or cuboid, can produce a variety of user requirements specifications and high-side box and the rectangular tube. 
 1. Uses: square box used parts of parallelism, perpendicularity and other inspection and marking. Square box is made of cast concrete six cube face of the cavity, one of the working surface of a V-groove. Square box test of the environmental conditions: temperature, humidity. 
 2 requirements: square box of the face can not have rust, scratches, cracks, dents and other defects affecting measurement performance. Non-face should be painted sand, edge chamfering. There should be signs in the square box wall, and marked with size dimensions, level serial number, manufacturer name. 
 3 Accuracy: developed for scraping flat square box in addition to test-givers, but also contacts with the coloring method test spots. Side length of 25mm in any number of spots within a square: 1, 2 less than 25 points; 3 less than 20 points.