A closely coiled helical spring is of mean diameter (D) and spring wire diameter (d). The spring index is the ratio of

A. Single B. Double C. Both A and B D. None of these

A. Equal to B. Less than C. Greater than D. None of these

A. $$\frac{{{\text{w}}l}}{6}$$ B. $$\frac{{{\text{w}}l}}{3}$$ C. $${\text{w}}l$$ D. $$\frac{{2{\text{w}}l}}{3}$$

A. Short columns B. Long columns C. Weak columns D. Medium columns