Uses in the spare part parallelism, the verticality examination and the lineation, the multi-purpose side boxes use in examinin iron straightedges:AVAILABLE IN GRADE :1,2&3SIZES FROM(MM) :100 150 200 250 300 350 400 500 600 SAME PRODUCEMagnetic Square Box Use:Be the same as general square box.Advantages:The V-shape slot has magnetic force .It is convenient for use