The parallel block are for precision machining and measuring The details of our parallel blocks are given below;Hardness: 55-62.Parallelism:0.005mm.Various series:PB161: 9 pairs: 100x5,6,8...;150x12,16,18...PB150: 14 pairs: 150x8,10,....x14PB151-1PB153PB155Please inform the details of your request when ordering.Wooden box package.