The Wahl's stress factor (K) for springs is given by (where )

• A. <img src="/_files/images/mechanical-engineering/machine-design/592-424-1.png">
• B. <img src="/_files/images/mechanical-engineering/machine-design/592-424-2.png">
• C. <img src="/_files/images/mechanical-engineering/machine-design/592-424-3.png">
• D. <img src="/_files/images/mechanical-engineering/machine-design/592-424-4.png">