This document discusses the parts of a screw gauge and how to use one. It identifies the main parts as the pitch scale, ratchet, circular scale, and anvil. It explains that the pitch scale measures the distance the screw travels and the circular scale helps determine measurements smaller than the scale's divisions. When using a screw gauge, the reading is taken as the linear scale reading plus the coinciding circular scale reading multiplied by the least count. The document also covers zero error and how to perform measurements with a micrometer screw gauge.

1. Dr. Y. P. Singh
S. R. Govt. Polytechnic College, Sagar (MP), India
Email: ypsingh@srgpcsagar.org
9425436423

4. Parts of a Screw Gauge
1. Pitch Scale

5. Parts of a Screw Gauge
• The head of the screw has a ratchet which avoids undue tightening
of the screw.
2. Ratchet

6. Parts of a Screw Gauge
• On the thimble there is a circular scale known as head scale which
is divided into 50 or 100 equal parts. When the screw is worked,
the sleeve moves over the pitch scale.
3. Circular Scale

7. Parts of a Screw Gauge
• A stud with a plane end surface is anvil which is fixed on the
‘U’ frame. When the tip of the screw is in contact with the anvil,
usually, the zero of the head scale coincides with the zero of the
pitch scale.
4. Anvil

9.  it is the smallest reading which you can get with the
instrument.

11. In Screw Gauge,
Total distance covered in 1 rotation = 1mm
Total divisions in screw scale = 10
Therefore,
L.C. = 1mm/ 10 = 0.01 mm
Or
L.C. = 0.001 cm

12. Zero error of Screw Gauge
If on touching the tip of the screw
with the stud, the zero mark of the
head scale coincides with the zero
mark of the base line, the
instrument is free from zero error.
There are two kinds of zero error:
(i) Positive zero error and
(ii) Negative error.

14. Positive Zero error of Screw Gauge
if the zero mark of the head
scale remains below the base
line of the main scale, the zero
error is said to be positive.

16. Negative Zero error of Screw Gauge
On the other hand, if on
touching the tip of the screw B
with the stud A, the zero of the
head scale goes above the base
line of the main scale, the zero
error is said to be negative

18. Use of A Micrometer Screw Gauge

19. Where can you use a micrometer screw gauge?

20. Reading an screw gauge.
• Read the reading on the linear scale reading and add with
coinciding circular scale multiply by least count.
Reading = Linear scale reading + (Coinciding circular scale x
Least count) = 2.5 mm + (46 x 0.01)
= (2.5 + 0.46) mm = 2.96 mm

21. MCQs

22. MCQs

23. MCQs

24. MCQs

25. MCQs

26. MCQs

27. Further Study
Further study through animation and simulator can be done at:
amrita.olabs.co.in,. (2015). Screw Gauge. Retrieved 28 December 2015,
from amrita.olabs.co.in/?sub=1&brch=5&sim=156&cnt=470