Correct option is C
Knuckle thread: The shape of the knuckle thread is not trapezoid, but it has a rounded shape. It has limited applications. It is used for valve spindles, railway carriage coupling, hose connections etc. Angle of knuckle thread is 30°.
Trapezoidal threads: These threads have a profile which is neither square nor V thread form and have a form of trapezoid. Different forms of trapezoidal threads are ACME thread, Buttress thread, Saw-tooth thread, Worm thread
ACME thread: It has an included angle of 29°. These are used in lathe lead screws.
Buttress Thread: In this thread, one flank is perpendicular to the axis of the thread and other flank is at 45°. These threads are used in power press, carpentry vices, gun breeches, ratchets etc.
