Standard Profiles Of Screw Threads

Thread profile on an electric bulb:

In a screw thread, theoretical depth (D) of the thread will be equal to ____

Identify the correct statement for the screw threads
A. A square thread of nominal diameter =30 mm and pitch =6 mm is designated as K 30 x 6.
B. Knuckle threads are used on necks of glass bottles.
C. Square threads offers less frictional resistance.
D. The angle between flacks of metric threads is 55⁰
E. The flacks of B.S.W. thread are equally rounded at both crest and root.
Choose the correct answer from the options given below:

In Turnbuckles joint, the two rods have ____ screw threads.