Simplest Explanations on the internet - What is K Factor and what is the terminology? 

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Terminology
Bend Allowance - The length of the arc through the bend area at the neutral axis.
Bend Angle - The included angle of the arc formed by the bending operation.
Bend Compensation - The amount by which the material is stretched or compressed by the bending operation. All stretch or compression is assumed to occur in the bend area.
Bend Lines - The straight lines on the inside and outside surfaces of the material where the flange boundary meets the bend area.
Inside Bend Radius - The radius of the arc on the inside surface of the bend area.
K-factor - Defines the location of the neutral axis. It is measured as the distance from the inside of the material to the neutral axis divided by the material thickness.
Mold Lines - For bends of less than 180 degrees, the mold lines are the straight lines where the surfaces of the flange bounding the bend area intersect. This occurs on both the inside and outside surfaces of the bend.
Neutral Axis - Looking at the cross section of the bend, the neutral axis is the theoretical location at which the material is neither compressed nor stretched.
Set Back - For bends of less than 180 degrees, the set back is the distance from the bend lines to the mold line.