I will define this. I have, if this is my propeller axis and my propeller blade starts from here,
let us say this is the boss, what will be the thickness at the root? We have just discussed the
thickness of the root will be highest, have to be reduce to the tip. Normally, it is a straight line
distribution, but you need not have a straight line distribution you can have a different
distribution, but conventionally it is a straight line that is, if the tip thickness is so much, root
thickness is so much, then we can join it by means of a straight line to get the thickness at any
other radius. If this is the thickness distribution, I extend this line to the propeller axis, and
this thickness at the propeller axis if the blade was extended to the axis is defined as root
thickness, not root, thickness at the axis, t0.