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BA AND G SERIES THREAD GAUGES

BA SERIES
Gauges for testing threads having a full form BA profile are manufactured to BS 93: 1951, and BS 919: Part 2: 1971.
BS 93 specifies basic information for the British Association thread form, and tabulates diameters for threads from 0BA to 25BA. However, 10BA is generally the smallest size manufactured as stock items. (Smaller sizes may be quoted for on application).

Basic form BA Thread

H= 1.136 34 x p h=0.600 00 x p
r=0.180 83 x p s=0.268 17 x p

External threads from OBA to 10BA are provided with an allowance of 0.001” on diameter to allow for easy assembly with the internal thread.
Provision is made for two classes of fit for external threads. Close and Normal for sizes from OBA to 10BA inclusive, and for Normal class only for sizes from 11BA to 16BA. Close class is intended for precision parts where there is controlled accuracy of form and pitch. Normal class is intended for general commercial use.
There is only one class of fit for internal threads, which is not designated.
BS 919: Pt 2:1971 specifies the limits for gauges, and are similar in style to those used for Whitworth threads.
G SERIES
Gauges for testing threads to
BS 2779: 1986 (G Series).
BS 2779 specifies details of pipe threads where pressure tight joints are not required, and also specifies the limits for gauges for testing the
product thread.
BS 2779 is technically equivalent to ISO 228/1 - 1982 for the designation, dimensions and tolerances of the product thread, and to ISO 228/2 - 1980, for verification by means of limit gauges.
The standard specifies basic information for Whitworth form fastening pipe threads, and tabulates diameters having a thread size designation in the range 1/16 to 6 inclusive.
The basic thread form is the Whitworth profile. (As shown on previous page).
There is no allowance provided for external or internal threads.
Provision is made for two classes of fit for external threads. Class A and Class B, and one class only for the internal thread, which is not designated. The external class A tolerance is equivalent to the internal thread tolerance. The class B tolerance is twice that of the class A tolerance.
Internal and external threads are designated by the letter G followed by the thread size designation. This designation refers to the pipe size and not to the thread diameter.
The gauge limits and principles are similar to the limits specified in
ISO 1502, and are somewhat different to the limits for Whitworth gauges specified in BS 919:Pt2:1971.

Screw Plugs
Screw Rings
Calipers
Size G0 NOGO 'E' Go NOGO ROLLER KNIFE
BA SERIES
0BA 0210 0211 0210A 0920 0921 1880 2080
1BA 0212 0213 0212A 0923 0924 1881 2081
2BA 0214 0215 0214A 0925 0926 1882 2082
3BA 0216 0217 0216A 0927 0928 1883 2083
4BA 0219 0220 0219A 0929 0930 1884 2084
5BA 0222 0223 0222A 0931 0932 1885 2085
6BA 0224 0225 0224A 0934 0935 1886 2086
7BA 0227 0228 0227A 0937 0938 1887 2087
8BA 0230 0231 0230A 0939 0940 1888 2088
9BA 0232 0233 0232A 0942 0943 1889 2089
10BA 0234 0235 0234A 0944 0945 1890 2090
11BA 0237 0238 0237A 0946 - 1891 2091
12BA 0239 0240 0239A 0947 - 1892 2092

G1/8 0180N 0181N 0180AN 0960N 0961N/0962N 1860 2060
G1/4 0182N 0183N 0182AN 0963N 0964N/0965N 1861 2061
G3/8 0184N 0185N 0184AN 0966N 0967N/0968N 1862 2062
G1/2 0186N 0187N 0186AN 0969N 0970N/0971N 1863 2063
G5/8 0188N 0189N 0188AN 0972N 0973N/0974N 1864 2064
G3/4 0190N 0191N 0190AN 0975N 0976N/0977N 1865 2065
G7/8 0192N 0193N 0192AN 0978N 0979N/0980N 1866 2066
G1 0194N 0195N 0194AN 0981N 0982N/0983N 1867 2067
G11/4 0196N 0197N 0196AN 0984N 0985N/0986N 1868 2068
G11/2 0198N 0199N 0198AN 0987N 0988N/0989N 1869 2069
G13/4 0200N 0201N 0200AN 0990N 0991N/0992N 1870 2070
G2 0202N 0203N 0202AN 0993N 0994N/0995N 1871 2071

 

The specification states that where no class is specified,
class B should be assumed.

 The regular checking of gauges in constant use is important, and should be carreid out as discribe on previous pages