When looking at carbide endmills, you will see a specification for shank diameters called H6. This from the ISO-286-2 tolerances for shafts. For our 1/2" example, the standard says within the shaft diameter range of 10-18mm the tolerance is +0/-11 microns which converts to +0.0000/-0.000433".
Most carbide endmill manufacturers purchase pre-ground carbide rod already cut to length with a chamfer on one end that will be the shank end. Below is a sampling of ten 1/2" rod blanks measured at three points. Blue is the chamfer/shank end, red is the middle and green is the cutter end.
To meet the H6 tolerance, the rod cannot be under 0.499567". Blank #1 exceeds the tolerance only on the shank end and should be rejected. Blank #8 does not exceed the tolerance on the blank end, but is up against it on the cutter end and middle.
Some manufacturers have tighter shank tolerances of H5 (+0/-0.000315) and H4 (+0/-0.000197). Again these were for a 1/2" shank.
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