In screw threads drawing, SQ 40 × 3 indicates:

Question

Question

This question was previously asked in

APPSC Lecturer (Polytechnic Colleges) Held on March 2020

Answer 1

Explanation:-

There is a particular method of the designation of threads:

Square threads:

Single start:

Square thread is designated by the letter Sq followed by nominal diameter and the pitch expressed in mm and separated by sign ×.
For eg. Sq 40 × 3

Multiple starts:

Multiple square threads are designated by the letter Sq followed by nominal diameter and the lead expressed in mm and separated by sign × and in brackets letter P followed by the pitch expressed in mm.
For eg. Sq 40 × 14 (P7)
\(No. of\;starts=\frac{Lead}{Pitch}\)

Hand:

Sometimes, the hand of the thread is given i.e Left hand (LH) and right hand (RH). It is written at the end.
For Eg. Sq 30 × 16 (P8) RH

Trapezoidal thread:

F1 Ashik Madhu 28.08.20 D10

In the trapezoidal thread, Sq is replaced by Tr.

For eg. Tr 30 × 16 (P8) RH

Important Point

Thread	Features
V thread	Larger contact area. Providing more frictional resistance. Not suitable for power transmission.
Square	Transmit power in both directions. Square thread is an ideal thread for power transmission. No radial pressure on the nut and motion is uniform. Difficult to manufacture. Less load carrying capacity due to less thickness at core diameter.
Trapezoidal	Transmit power in both directions Radial pressure is present and affects performance. Efficiency is less than a square thread. They are economical to manufacture due to the use of a multi-point cutting tool. High load-carrying capacity due to its greater thickness at core diameter.
Acme	It is a modified form of trapezoidal thread. Thread angle is 29°.
Buttress	It is used where the heavy axial force acts along the screw axis in one direction only. Stronger than square and trapezoidal thread. Higher efficiency compared to trapezoidal.

Fitter 35 25Q Hindi - Final images Q8