# Screw Gauge

Experiment No :2

Aim: To measure the i)Thickness of the Glass Plate ii) Diameter of the metal wire iii) Volume of the given Glass Plate.

Apparatus : Screw Gauge , Glass Plate and Metal wire .

Description : Screw Gauge consists of  U shaped metallic frame.To one side of this U frame a long hallow cylindrical tube with a nut inside it, the inner side of cylindrical nut contains a uniform thread cut in it.On the other side of U frame a fixed stud $S_1$ with a plane face is attached.

A screw $S_2$ is fitted in the cylindrical nut.One side of the screw $S_2$ has a plane face similar to that of stud $S_1$. The faces of $S_1$ and $S_2$ are plane and parallel to one another. The other end of the screw $S_2$ carries a milled head ‘H’ attached to a cap ‘C’ with a sloping edge. When the head H is rotated, the screw moves ”to and fro” in the nut.The milled head H is provided with a safety device ‘D’ to rotate the head H.When the object is held between the stud $S_1$ and  screw $S_2$  and the head H is rotated using the safety device (D), it produces crackling sound when optimum pressure is applied on the object.

The outer surface of long cylindrical nut consists of a thick horizontal line ‘P’ parallel to the axis of cylindrical tube.This line ‘P’ is called Index line. Along the index line a scale is graduated in millimeters.This scale is called Pitch Scale.On the sloping edge of the cap ‘C’ a circular scale is graduated, which consists of 100 equal divisions, this scale is called Head scale.

Theory : The screw gauge works on the principle of screw.

When we rotate the head ‘H’ by means of safety device ‘D’ through one complete rotation, the distance moved by the screw for every complete rotation is constant. This constant distance moved by the screw for one complete rotation of head ‘ H ‘ is called Pitch of the screw.If the head scale has 100 equal divisions, then the distance moved by the screw for even 1/100 of a complete rotation can be measured accurately,this is called Least count of screw gauge.

Therefore Least count (L.C) = $\frac{Pitch of the screw}{Number of divisions on Head scale}$ .

Procedure :First we have to determine the least count of the given Screw gauge.

To determine the least count of the screw gauge, the head ‘H’ is rotated through certain (say 5) number of complete rotations.The distance moved by the sloped  edge over the pitch scale is measured.

Now substitute these values in the formula of pitch of the screw = $\frac{Distance moved by sloped edge over the pitch scale}{Number of rotations of the screw}$.

Least count L.C =  $\frac{Pitch of the screw}{Number of divisions on Head scale}$ .

Now check whether the given screw gauge has any ZERO ERROR or not. To determine the ZERO ERROR, the head H is rotated until the flat end of the screw $S-2$ touches the plane surface of the stud $S_1$ (do not apply excess pressure) i.e we have to rotate the head only by means of safety device ‘D’ only.

When $S_1$ and $S_2$ are in contact,the zero of the head scale perfectly coincides with the index line as in Fig-(a). In such case there will be no ZERO ERROR and no correction is required.

When $S_1$ and $S_2$ are in contact,the zero of the head scale is below the index line as in Fig(b), such ZERO ERROR is called positive ZERO ERROR, and the correction is negative.

When $S_1$ and $S_2$ are in contact,the zero of the head scale is above the index line as in Fig(c) , such ZERO ERROR is called negative ZERO ERROR, and the correction is positive.

a) Determine the thickness of glass plate : The given object glass plate is held between the two parallel surfaces of fix stud $S_1$ and screw tip $S_2$. Note the completed number of divisions on pitch scale, which is called PITCH SCALE READING (P.S.R). The number of the head scale division coinciding with the index line is noted, which is called OBSERVED HEAD SCALE READING  n’. If the given screw gauge has ZERO ERROR (x) the correction is made by adding or subtracting the ZERO ERROR (x) from the  OBSERVED HEAD SCALE READING  n’.The corrected value (n’-x) or (n’+x)  is called the HEAD SCALE READING (H.S.R) n.

To calculate the fraction the H.S.R (n) is multiplied by the least count (L.C).

Thickness of the Glass plate = Total reading = P.S.R +$n\times L.C$ – - -  – - (1)

Changing the position of glass plate , 5 readings should be taken, and recorded in the table-1. Every time calculate the total thickness of the glass plate using equation (1).

Average of the 5 readings  of the glass plate should be calculated, to get the average thickness(t) of the given glass plate.

b) Determine the radius(r) of the given metal wire :The given object metal wire is held between the two parallel surfaces of fix stud $S_1$ and screw tip $S_2$. Note the completed number of divisions on pitch scale, which is called PITCH SCALE READING (P.S.R). The number of the head scale division coinciding with the index line is noted, which is called OBSERVED HEAD SCALE READING  n’. If the given screw gauge has ZERO ERROR (x) the correction is made by adding or subtracting the ZERO ERROR (x) from the  OBSERVED HEAD SCALE READING  n’.The corrected value (n’-x) or (n’+x)  is called the HEAD SCALE READING (H.S.R) n.

To calculate the fraction the H.S.R (n) is multiplied by the least count (L.C).

Diameter of the given wire = Total reading = P.S.R +$n\times L.C$

Changing the position of metal wire, 5 readings should be taken, and recorded in the table-2. Every time calculate the total diameter (d) of the metal wire using equation (1).

Average of the 5 diameter of the metal wire should be calculated, to get the average diameter(d) of the given metal wire.

Radius (r) of the metal wire =$\frac{d}{2}$ mm.

Precautions : i ) Pitch scale reading (P.S.R) should be taken carefully without parallax error ii ) Head scale reading (H.S.R) should be taken carefully without parallax error iii )Screw must be rotated by holding the safety device ‘D’ iv ) Do not apply excess pressure on the object held between the surfaces $S_1$ and $S_2$.

v ) The screw is rotated in only one direction either clock wise or anti-clock wise to avoid the back lash error.

Observations : i ) Zero error =

ii) Zero correction =                   mm

iii ) Distance moved by the head for 5 complete revolutions =                         mm

iv ) Number of head scale divisions =

v) Pitch of the screw =$\frac{Distance moved by sloped edge over the pitch scale}{Number of rotations of the screw}$.

vi) Least count (L.C) =$\frac{Pitch of the screw}{Number of divisions on Head scale}$ .

Table -1 ( Thickness of glass plate ) :

 S.No Pitch Scale Reading (P.S.R) amm Observed H.S.R    (n’) Correction   (x) Corrected H.S.R  n=n’-x Fraction  b=n*L.C Total reading  (a+b) mm 1. 2. 3. 4. 5.

Average thickness of the glass plate (t) =        mm

Table – 2 (Diameter of the metal wire):

 S.No Pitch Scale Reading (P.S.R) amm Observed H.S.R    (n’) Correction   (x) Corrected  H.S.R n=n’-x Fraction  b=n*L.C Total reading  (a+b) mm 1. 2. 3. 4. 5.

Average diameter  d =       mm

Average radius r = $\frac{d}{2}$ =         mm .

c ) Volume of Glass plate (v) : The length ( l ) , breadth ( b) are determined using vernier calipers and thickness ( t ) of the glass plate is determined using screw gauge. The values of l ,b and t are substituted in the equation of volume  V = ( l )( b )( t )    $mm^3$

Watch this video to get idea about Screw Gauge :

## 128 thoughts on “Screw Gauge”

1. yogendra

wonderful explanation

2. it would have been better if there were some java based animations

3. Sid

superb explanation thnx a lot
get it going

4. k.m.sarma

Simply excellent

5. It is really very good exp. but i request the author to explain by taking one example so that student know how to do the calculation

6. dharshana

it gave me the exact answer i was looking for(principle of screw gauge)thanks a lot

8. anees . v .a

excellent. this is what i exactly need. thankyou.

9. shreethi

thanks a lot… but can u just give an example and show the calculation..??

10. gyaunnrraje

Ex i) Suppose we are dividing 49 MSD in to 50 VSD
1MSD =1mm
The principle of vernier is 50 VSD =49 MSD,
1 VSD = 49/50 MSD
Least Count = 1 MSD – 1 VSD
= 1 MSD -(49/50) MSD = (1/50) MSD
= 0.02 mm
Ex ii) Ex i) Suppose we are dividing 99 MSD in to 100 VSD
1MSD =1mm
The principle of vernier is 100 VSD =99 MSD,
1 VSD = 99/100 MSD
Least Count = 1 MSD – 1 VSD
= 1 MSD -(99/100) MSD = (1/100) MSD
= 0.01 mm

11. sudha

least count for screw gauge

12. gyaunnrraje

For Detailed Calculation go to “Question No:3 of practical Exams Question bank”.

13. Pingback: Contents 1 « A to Z of Physics

14. scarlet

Nice work!!!

15. hai

16. screw gauge experiment is very good

17. nice explanation…….thanks

18. anurag

thanks,this was exactly what i needed

19. it’s a nice instrument 2 measue
isn’t it

20. v kameswara rao

good. can be made more simple without loss of content

21. prajith

thanks,this was exactly what i needed
keep up the good work

22. Simply Fabulous for we like Science students. Ihave score 90 and now I expect more

23. sir i want an example to deriving this Screw Gauge practical

24. Neha Nasim

Sir i want applications of screw gauge.

25. anand kumar

why slope edge is called head scale ?

26. kapoor

its really nice explanation i got all my answers ….really its satisfactory …thanx

27. praful

its very funtastic yar…………………

28. shobha.N.C

Its too good. explanation part is very clear to understand. i feel that their should also be a numerical example of zero error and calculation part such that students can easily understand.

29. Sumanth

Great work..,Thanks a lot.., Thank u sir for responding to our quests..,Hope that u might continue..,

30. A ANUSHA

it is really very good.easy to understand.i got all my answers thank u.

31. ekanatha chavan

good

32. it was very very useful for me

33. ujjwal

what is the function of this…

34. shoieb

what is the least count

35. Yatendra

Thanx…This is awesome…
Today is my practical and u saved me…

36. Gurpreet

I like d the way of teaching

37. sameer

yea,, nice description abt the micrometer,, and the pictures really helped me a lot,, thankyou

38. thanks alot…it helped in my project

39. kalyan

excellent way of explanation sir.

40. rojarani

good i need much information

41. what is the values?

42. gyaunnrraje

The minimum length which can be measured by the device is called it’s least count

43. gyaunnrraje

Screw Gauge is used to measure the thickness of thin objects like glass plates,metal sheets and paper .Also used to measure the diameters or radius of thin wires.

44. Ankur pathak

Very good explanation

45. mani

i find it to be helpful being a first year student in an engineering college

46. nice exp

47. abhi

thia was so so helpful… thnx a ton!!! it helpd me a lot!!

48. vinay

why screw guage is ‘u’ shaped?

49. it is very useful website for learing

50. ajay sharma

it is very good to knw about the screw gauge and its measurement . this video is so owsem and i am able to nkw how to measure the screw gauge and its least count

51. its really infrmative……………it helped me out in d last moment………really gr8 job

52. ally

execellent

53. ally

excellent

54. Tarun Kumar

thnxxx a lot sir it was awesome.I tried a couple of lab manuals but this is simply unmatched. Hats OFF 2 U!!!

55. yasmeen banu

its really good… but it can be more fabulous if the author includes an example to explain it.

56. v.surendra reddy

exallent explanatiom

57. akshay

this was brilliant

58. Srujayvbabu

Good and thanks

59. Thisaru Mayura

Thanks.. helped alot

60. lovely!! i got d concept thanks!!

61. Sreedhar Rao Sonti, Dr.

elaborate, precise and concise to the point a student can understand without any ambiguity.

Thanks,it is very good explanation……………………

63. great exp

64. video give excellent description of screw gauge

very brief but useful

66. prakash

it is really good……it helped me a lot

67. screw gauge or micrometer very nice detail but fine accurecy calculation is dell.

68. nabil

helped me alot

69. it really helped me

70. sharath

thank u

71. sachin s m

okay …..but still it didnt clear my doubt about finding the zero error…..it should have been given with an example….

72. shashi

good explanation !

73. dhakshina

very good explanation thanks lot

74. Mg Win

Not enough.

75. sasi

excellent and nothing more to say

76. munna

its good but a practical is necessary to understand the whole thing

77. Amarjeet Kumar(bindass)

It is too much better for self understanding. I am extremly impressed wid the description and explanation.

78. nikhil

does the divisions of headscale and least count are constant for every screw gauge

79. shivek bittu

its exactly true i was looking for that……………..!

80. hari mahesh

I was looking for that good explanation !

81. hari mahesh

Ex i) Suppose we are dividing 49 MSD in to 50 VSD
1MSD =1mm
The principle of vernier is 50 VSD =49 MSD,
1 VSD = 49/50 MSD
Least Count = 1 MSD – 1 VSD
= 1 MSD -(49/50) MSD = (1/50) MSD
= 0.02 mm
Ex ii) Ex i) Suppose we are dividing 99 MSD in to 100 VSD
1MSD =1mm
The principle of vernier is 100 VSD =99 MSD,
1 VSD = 99/100 MSD
Least Count = 1 MSD – 1 VSD
= 1 MSD -(99/100) MSD = (1/100) MSD
= 0.01 mm

82. surya

i want observations…calculated values……

83. Aakash Ranjan

i think this is a wonderful explanation about this concept but still i think there is a need of example how to find the pitch of the screw. please

84. PRASANTH

IT’S VERY GOOD EXPLANATION TO GOOGLE SEARCHING STUDENTS

85. PRASANTH

THANK Q SOMUCH

86. very nic eeeeeee

it helps me very much
thanx

88. Srutanwita Mukherjee

it has been very helpfull…. thank you

89. gooooo thing!!!!!!!!!!!!!!!!!!!!!!!!!

90. manoj kumar tn

much better explanation than our teachers

91. Sudip mishra

Thnks sooo much ur pratical is saved me

92. aman

Nice Video THANKS…..

93. he should show us the calci once

94. Great…

95. i like this by V.Surya and S.Anis

96. suhail khan

excelant

sooooooooooooooo interestive

97. t.vicky

screw gauge is a very ,,,,,,,,,, easyyyyyyy.
i will do experiment it is easyyyyyyy.

98. Robin james

Supper

99. Robin james

Like

100. Rifat Hayat Khan

good explaination

101. Vipin sen

Accha haiB-)

102. Misba

It cleared all my doubts! Thanks a BUNCH!!! It was of great help!

103. GURU

should have explained about positive and negative errors

104. ramesh

easy learning

105. aswani

screw gauge is very very simple device

106. ver good explanation

107. this website is so usefull in students thanking you google

108. sourabh

great explanation………. good……….

109. poorva

amazing explanation

110. AnWaR

111. vyshnavi

it is sooooooooo nice and i learned a loooooooooooooot

112. yeswanyh

i learnt a lot and the lesson is in detail

113. naveenreddy

114. shayari

I am sooooooo thankfull..

115. Rameeza Sayed

very useful …….thank u 4 efforts like this

116. chinay panchal

it is nicely and easy explained with labelled diagram thank you for it…………………

117. Shubhay Raj Dubey

It gave correct reply for my problem& hence helped me a lot

118. sandhya rani

excellent explanation

119. vaishnavi

this explanation is nice…………

120. Athira Ashok

It helped me to understand in easy way.

121. narayani

exact explanation!!!!

122. amir ali khan

This is a parfact explanation

123. surthi

it was good

124. martin

when the msd lies in 48, what is the zero error

125. akash

pls improve the information and it is cool

126. sreyasee

i got d actual ans ,I was finding of. Thaaaaaaannnnnnnxxxxxxxxxxx.

127. vicky

superb explanation I just loved it very much I think u guys better to open a application