It is a interesting specification for hardness. There are three different hardness values (spec?) listed. 1 Nominal Value. 2. Mean valve of 20 particles. 3. limit values of the 20 individual particles. Each size of shot has three Nominal hardness values, with each having a range of hardness values for 2 and 3 above. The three nominal values correspond to three types of rod used to make the cut wire shot.
After all of that, I can not tell you why they have done this other than they must have data to support differences in work created by these slight changes in hardness.
Or, this is the resulting hardness of drawing the wire to the correct size.
I look forward to hearing if someone who is involved in the "Association of German Spring Industries" that controls this document has some information to share.
