a. I have learnt -Torsional rigidity, Breaking twist, Shear modulus. 

 b. The twist for breaking of a yarn is called breaking twist. It also can be defined as the number of twists required to break a yarn. Breaking twist depends on the diameter of fiber and it is inversely proportional to its diameter. 

 That is, 

 Tb ∞ 1/d 

 Where, 

 Tb = Breaking twist,

 d = diameter of fiber.