• A thread is formed by cutting a continuous helical groove on a cylindrical surface. • A threaded joint mainly composed of two elements ,a bolt and nut. The screwed joints are widely used where the machine parts are to be readily connected or disconnected without damage to the machine or the fastening.
Advantages and disadvantages Adv. 1. Screwed joints are highly reliable in operation. 2. Screwed joints are convenient to assemble and disassemble. 3. Screwed joints are relatively cheap to produce due to standardization and highly efficient manufacturing processes. Disadv. 1. Stress concentration in the threaded portions which are the weak points under variable load condition.
Important parts of screw thread
Various parts of the screw Major diameter. It is the largest dia meter of an external and internal screwed thread. The screw is specified by this diameter. Minor diameter. It is the smallest diameter of an external or internal screw thread. Also known as root dia or core dia. Pitch dia. It is the diameter of imaginary cylinder, which pass through the thread at such points make equal width of the thread and the width of the spaces between the threads. Pitch. It is distance between two consecutive crest or trough. Lead. Distance which a screw thread advances axially in one rotation of the nut.