The vise shown utilizes two double$-$threaded screws, each with a

mean radius of $0\mathrm{.}25$ in and a pitch of $0\mathrm{.}08$ in $.$ The lower member

is threaded at both A and B with ${}_s=0\mathrm{.}35$ while the upper

member is not threaded. Screw B is adjusted to provide the

correct spacing between the members and then screw $A$ is

tightened to produce the clamping force. If the wood blocks are

to be clamped with a force of $120$ lb $,$ what couple needs to be

applied to screw $A?$