BS 970 (l991) Tolerances for cold drawn / turned bar
Section Size Permitted variation
Round Drawn
6 18mm
+0 to -0.070 mm (0.0028")
>18 30mm
+0 to -0.085 mm (0.0033")
>30 50mm
+0 to -0.100 mm (0.0039")
>50 80mm
+0 to -0.120 mm (0.0047")
>80 100mm
+0 to -0.140 mm (0.0055")
Round Turned
>80 120mm
+0 to -0.140 mm (0.0055")
>120 180mm
+0 to -0.160 mm (0.0063")
>180 250mm
+0 to -0.185 mm (0.0073")
>250 315mm
+0 to -0.210 mm (0.0083")
Square and hexagon Drawn
6 18mm
+0 to -0.090 mm (0.0035")
>18 30mm
+0 to -0.110 mm (0.0043")
>30 50mm
+0 to -0.130 mm (0.0051")
>50 80mm
+0 to -0.160 mm (0.0063")
>80 105mm
+0 to -0.250 mm (0.0098")
Flat (width) Drawn
<18mm
+0 to -0.110 mm (0.0043")
>18 30mm
+0 to -0.130 mm (0.0051")
>30 50mm
+0 to -0.160 mm (0.0063")
>50 80mm
+0 to -0.190 mm (0.0075")
>80 100mm
+0 to -0.220 mm (0.0087")
>100 130mm
+0 to -0.350 mm (0.0138")
>130 160mm
+0 to -1.00 mm (0.0394")
>160 320mm
+0 to -2.00 mm (0.0787")
Flat (thickness) Drawn
<18mm
+0 to -0.110 mm (0.0043")
>18 30mm
+0 to -0.130 mm (0.0051")
>30 50mm
+0 to -0.250 mm (0.0098")
>50 80mm
+0 to -0.350 mm (0.0138")



BS 970 (1991) Tolerances for hot rolled and rough turned bar
Section Size Diameter +/- mm Out of section *a
Rounds >76 90 mm 1.3 mm 2.0 mm
>90 120 mm 1.5mm 2.3 mm
>120 160 mm 2.0 mm 3.0 mm
>160 200 mm 2.5 mm 3.8 mm
>200 mm 3.0 mm 4.5 mm
Definition (*a), The difference between the maximum & minimum diameter of the bar measured at the same cross section.



BS 970 (1991) Straightness tolerances
Section Steel grade Permitted variation
Rounds <0.25 % carbon 1 in 1000
0.25 % carbon, alloys & all heat treated grades 1 in 500
Squares and Hexagons <0.25 % carbon to 75mm
over 75mm
1 in 750
1 in 500
0.25 % carbon, alloys & all heat treated grades 1 in 375
Flats <0.25 % carbon 1 in 500
0.25 % carbon, alloys & all heat treated grades 1 in 375
Permitted variation shall be measured as a maximum deviation from straightness in any 3000mmm portion of the bar.