| CLASS
OF FIT |
|
Plug
gauges
(Internal)
|
Ring
gauges
(External)
|
Application
|
|
1B
|
1A
|
Where
quick assembly is needed even when threads are
dirty / damaged wide tolerances for male and female
threads.
|
|
2B
|
2A
|
Corresponds
to medium fit and used for general applications
which requires free assembly.
|
|
3B
|
3A
|
Where
closer fit is required.
|
|
| DIAMETER
– PITCH COMBINATION |
| Diameter
– TPI combination not covered in this table as well
as for all diameters above 6" use "UNS" series irrespective
of TPI. |
|
Dia
Inch
|
Dia
MM
|
UNC
|
UNF
|
UNEF
|
UN
|
| No.
0 |
1.524
|
-
|
80
|
-
|
-
|
| No.
1 |
1.8542
|
64
|
72
|
-
|
-
|
| No.
2 |
2.1844
|
56
|
64
|
-
|
-
|
| No.
3 |
2.5146
|
48
|
56
|
-
|
-
|
| No.
4 |
2.8448
|
40
|
48
|
-
|
-
|
| No.
5 |
3.175
|
40
|
44
|
-
|
-
|
| No.
6 |
3.5052
|
32
|
40
|
-
|
-
|
| No.
8 |
4.1656
|
32
|
36
|
-
|
-
|
| No.
10 |
4.826
|
24
|
32
|
-
|
-
|
| No.
12 |
5.4864
|
24
|
28
|
32
|
-
|
| ¼"
|
6.350
|
20
|
28
|
32
|
-
|
| 5/16"
|
7.9375
|
18
|
24
|
32
|
20,28
|
| 3/8"
|
9.525
|
16
|
24
|
32
|
20,28
|
| 7/16"
|
11.1125
|
14
|
20
|
28
|
16,32
|
| ½"
|
12.700
|
13
|
20
|
28
|
16,32
|
| 9/16"
|
14.2875
|
12
|
18
|
24
|
16,20,28,32
|
| 5/8"
|
15.8750
|
11
|
18
|
24
|
12,16,20,28,32
|
| 11/16"
|
17.4625
|
|
|
24
|
12,16,20,28,32
|
| ¾"
|
19.050
|
10
|
16
|
20
|
12,28,32
|
| 13/16"
|
20.6375
|
|
|
20
|
12,16,28,32
|
| 7/8"
|
22.225
|
9
|
14
|
20
|
12,16,28,32
|
| 15/16"
|
23.8125
|
|
|
20
|
12,16,28,32
|
|
Dia
Inch
|
Dia
MM
|
UNC
|
UNF
|
UNEF
|
UN
|
| 1"
|
25.400
|
8
|
12
|
20
|
16,28,32
|
| 1.1/16"
|
26.9875
|
|
|
18
|
8,12,16,20,28
|
| 1.1/8"
|
28.575
|
7
|
12
|
18
|
8,16,20,28
|
| 1.3/16"
|
30.1625
|
|
|
18
|
8,12,16,20,28
|
| 1.1/4"
|
31.750
|
7
|
12
|
18
|
8,16,20,28
|
| 1.5/16"
|
33.3375
|
|
|
18
|
8,12,16,20,28
|
| 1.3/8"
|
34.925
|
6
|
12
|
18
|
8,16,20,28
|
| 1.7/16"
|
36.5125
|
|
|
18
|
6,8,12,16,20,28
|
| 1.1/2"
|
38.100
|
6
|
12
|
18
|
8,16,20,28
|
| 1.9/16"
|
39.6875
|
|
|
18
|
6,8,12,16,20
|
| 1.5/8"
|
41.275
|
|
|
18
|
6,8,12,16,20
|
| 1.11/16 |
42.8625
|
|
|
18
|
6,8,12,16,20
|
| 1.3/4
|
44.450
|
5
|
|
|
6,8,12,16,20
|
| 1.13/16
|
46.0375
|
|
|
|
6,8,12,16,20
|
| 1.7/8
|
47.625
|
|
|
|
6,8,12,16,20
|
| 1.15/16
|
49.2125
|
|
|
|
6,8,12,16,20
|
| 2
|
50.800
|
4.5
|
|
|
6,8,12,16,20
|
| 2.1/8" |
53.975
|
-
|
-
|
-
|
6,8,12,16,20
|
| 2.1/4" |
57.150
|
4.5
|
-
|
-
|
6,8,12,16,20
|
| 2.3/8" |
60.325
|
-
|
-
|
-
|
6,8,12,16,20
|
| 2.1/2" |
63.500
|
4
|
-
|
-
|
6,8,12,16,20
|
| 2.5/8" |
66.675
|
-
|
-
|
-
|
4,6,8,12,16,20
|
|
Dia
Inch
|
Dia
MM
|
UNC
|
UNF
|
UNEF
|
UN
|
|
|
| DIAMETER
– PITCH COMBINATION |
|
Dia
Inch
|
Dia
MM
|
UNC
|
UNF
|
UNEF
|
UN
|
| 2.3/4" |
69.850
|
4
|
-
|
-
|
6,8,12,16,20
|
| 2.7/8" |
73.025
|
-
|
-
|
-
|
4,6,8,12,16,20
|
| 3" |
76.200
|
4
|
-
|
-
|
6,8,12,16,20
|
| 3.1/8" |
79.375
|
-
|
-
|
-
|
4,6,8,12,16
|
| 3.1/4" |
82.550
|
4
|
-
|
-
|
6,8,12,16
|
| 3.3/8" |
85.725
|
-
|
-
|
-
|
4,6,8,12,16
|
| 3.1/2" |
88.900
|
4
|
-
|
-
|
6,8,12,16
|
| 3.5/8" |
92.075
|
-
|
-
|
-
|
4,6,8,12,16
|
| 3.3/4" |
95.250
|
4
|
-
|
-
|
6,8,12,16
|
| 3.7/8" |
98.425
|
-
|
-
|
-
|
4,6,8,12,16
|
| 4" |
101.60
|
4
|
-
|
-
|
6,8,12,16
|
| 4.1/8" |
104.775
|
-
|
-
|
-
|
4,6,8,12,16
|
| 4.1/4" |
104.950
|
-
|
-
|
-
|
4,6,8,12,16
|
| 4.3/8" |
111.125
|
-
|
-
|
-
|
4,6,8,12,16
|
| 4.1/2" |
114.30
|
-
|
-
|
-
|
4,6,8,12,16
|
| 4.5/8" |
117.475
|
-
|
-
|
-
|
4,6,8,12,16
|
| 4.3/4" |
120.650
|
-
|
-
|
-
|
4,6,8,12,16
|
| 4.7/8" |
123.825
|
-
|
-
|
-
|
4,6,8,12,16
|
| 5" |
127.000
|
-
|
-
|
-
|
4,6,8,12,16
|
| 5.1/8" |
130.175
|
-
|
-
|
-
|
4,6,8,12,16
|
| 5.1/4" |
133.350
|
-
|
-
|
-
|
4,6,8,12,16
|
| 5.3/8" |
136.525
|
-
|
-
|
-
|
4,6,8,12,16
|
| 5.1/2" |
139.700
|
-
|
-
|
-
|
4,6,8,12,16
|
| 5.5/8" |
142.875
|
-
|
-
|
-
|
4,6,8,12,16
|
| 5.3/4" |
146.050
|
-
|
-
|
-
|
4,6,8,12,16
|
| 5.7/8" |
149.225
|
-
|
-
|
-
|
4,6,8,12,16
|
| 6" |
152.400
|
-
|
-
|
-
|
4,6,8,12,16
|
|
| Above
6" Diameter use ‘UNS’ Series irrespective of TPI
|
|
| COATED
& UNCOATED THREADS |
| Following
table gives standard classes to be used or coating
allowance to be adjusted from standard dimensions.
|
|
Type
|
Before
coating
|
After
coating/
Uncoated finish threads.
|
Plugs
(Internal threads) |
1B
+ 0.025mm / 0.001"
2B + 0.025mm / 0.001"
3B + 0.025mm / 0.001"
|
1B,
2B & 3B
|
Rings
(External threads) |
1A/
2A
2A-0.025mm / 0.001"
i.e. 2AG
|
3A
2A
|
|
| 'AG'
Class for external threads (Ring gauges) |
|
For
lubricant and high temperature applications it
is necessary to maintain normal allowance for
after coating or Uncoated finish condition. For
these applications '2AG' class is recommended.
For '2AG' class the thread diameters are 0.001"
/ 0.025mm less than '2A' class. Even after coating
of 0.025mm / 0.001" the dimensions fall in '2A'
class. Thus maintaining the allowance.
If
for these applications, if '2A' class dimensions
are maintained Before coating. After coating dimensions
will fall in '3A' Class. For '3A' class the allowance
is zero and the required allowance will not be
maintained. In order to over come this problem
'2AG' class is recommended for these applications.
For '2AG' gauges BS specification should be followed.
|
| DESIGNATION
/ MARKING SYSTEM |
|
The
nominal diameter of the gauge is given in inches
or number series is used for smaller diameters.
'-' sign is used after diameter, which is followed
by threads per, inch i.e. TPI. Thread series and
class of fit is written after TPI. For Right Hand
threads it is not necessary to mention, but incase
of left Hand threads, 'LH' is written after class
of fit. e.g. ½"-13 UNC 2A
|
|
|
