The threads used for transmission of power is

Explanation:

Screws:

The screws are used to convert rotary motion into translatory motion.

Following are the types of screw threads mostly used:

Square thread

• A square thread is adapted for the transmission of power in either direction.
• This thread results in maximum efficiency and minimum radial or bursting pressure on the nut.
• It is difficult to cut with tap and dies.
• It is usually cut on a lathe with a single point tool and it cannot be easily compensated for wear.
• The square threads are employed in screw jacks, presses and clamping devices.

Acme or trapezoidal thread

• An acme thread is a modification of square thread.
• The slight slope given to its sides lowers the efficiency slightly than square thread.
• It also introduced some bursting pressure on the nut but increases its area in shear.
• An acme thread may be cut by means of dies and hence it is more easily manufactured than square thread.
• It is used where a split nut is required and where provision is made to take up wear as in the lead screw of a lathe.

Buttress thread

• A buttress thread is used when large forces act along the screw axis in one direction only.
• This thread combines the higher efficiency of square thread and the ease of cutting and adaptability to a split nut of an acme thread.
• It is stronger than other threads because of greater thickness at the base of the thread.
• The buttress thread has limited use for power transmission.
• It is employed as a thread for light jack screws and vices.

Knuckle thread

• A knuckle thread is another modification of square thread.
• The sharp corners of the square thread are rounded to make the crests and roots semicircular.
• The crests and the roots are tangent to each other.
• The profile is difficult to machine and hence these threads are usually manufactured by rolling or casting.
• Due to its unique shape, these threads are less subjected to wear and suitable for rough usage.
• Knuckle threads are provided on the coupler of the railway carriage, hydrants, glass bottles, electric bulbs, etc.