I disagree on precision....but then again I was a tool and die maker. I like to know where my tools are....
Whatever you get make sure they are the same height and you could also make sure the "v" is centered in the block. It just makes life simpler.
To do this use a granite plate, take a plug gage and clamp in in the "v" block. Using a height stand and indicator run the indicator ball over the plug gage and set zero. Check again. Take plug gage out of first "v" block and install in second block and run indicator over the plug gage. It SHOULD be the same, if not you know there is a difference in height.
To check centrality of "v" in block, take block with gage plug in it and lay it on it's side. Run indicator over plug gage and set zero. Turn block over 180 degrees to the other side and run indicator over it, it SHOULD read zero...if not...
I worked in a machine shop and QC would accept or reject parts seemingly on a whim. I had them check their "v" blocks this way and found one off a few thousands. Engineering 1, Quality 0...
