12 m and 12 m

12 m and 13 m

13 m and 12 m

13 m and 13 m

only (i)

(i)and(ii)

(ii) and (iii)

(i) and (iii)

height

foot width

head width

any of the above

head

web

foot

head and foot both

increase the lateral strength

increase the vertical stiffness

avoid the stress concentration

reduce the wear