$7.$ A key made from a cylindrical disc having segmental cross$-$section is known as: $-$ a$)$ wood$-$ruff key $-$ b$)$ feather key $-$ c$)$ flat saddle key $-$ d$)$ gib head key $-$ e$)$ hollow saddle key$\mathrm{.}8.$ A self$-$locking screw has: $-$ a$)$ fine threads $-$ b$)$ coarse threads $-$ c$)$ coefficient of friction $>$ tangent of load angle $-$ d$)$ hole for inserting split pin $-$ e$)$ two nuts for locking$\mathrm{.}9.$ A stud: $-$ a$)$ has a head on one end and a nut fitted to the other $-$ b$)$ has head at one end and other end fits into a tapped hole in the other part to be joined $-$ c$)$ has both the ends threaded $-$ d$)$ has pointed threads $-$ e$)$ requires locking nuts.