As you may know, in steel industry, there must be some dimension and sizes for one product or a project. And for each size of product, there will be some standard and tolerance requirements. Here in this post we share the different round steel bar tolerance requirements between BS 970-3 and ISO 286-2 standard.

round steel bar tolerance bs 970 vs iso 286

  1. Cold Drawn Round Steel Bar Tolerance &  Steel Hexagon, Flat Tolerance (BS 970-3)
Tolerances for Cold Drawn Bar
Section Size, diameter or width across flats Permitted variation
mm mm
Round ≥6 ≦ 18
> 18 ≦ 30
> 30 ≦ 50
> 50 ≦ 80
> 80 ≦ 100		 + 0 to – 0.070
+ 0 to – 0.085
+ 0 to – 0.100
+ 0 to – 0.120
+ 0 to – 0.140
Square and
hexagon		 ≥ 6 ≦ 18
> 18 ≦ 30
> 30 ≦ 50
> 50 ≦ 80
> 80 ≦ 105		 + 0 to – 0.090
+ 0 to – 0.110
+ 0 to – 0.130
+ 0 to – 0.160
+ 0 to – 0.250
Flat (width) < 18
> 18 ≦ 30
> 30 ≦ 50
> 50 ≦ 80
> 80 ≦ 100
> 100 ≦ 130
> 130 ≦ 160
> 160 ≦ 320		 + 0 to – 0.110
+ 0 to – 0.130
+ 0 to – 0.160
+ 0 to – 0.190
+ 0 to – 0.220
+ 0 to – 0.350
+ 0 to – 1.00
+ 1.00 to – 1.00
Flat (thickness) < 18
> 18 ≦ 30
> 30 ≦ 50
> 50 ≦ 80		 + 0 to – 0.110
+ 0 to – 0.130
+ 0 to – 0.250
+ 0 to – 0.350

2. Turned Round Steel Bar Tolerances (BS 970-3)

Tolerances for Turned Bars
Size, diameter Permitted variation
mm mm
≧ 6 ≦ 18
> 18 ≦ 30
> 30 ≦ 50
> 50 ≦ 80
> 80 ≦ 120
> 120 ≦ 180
> 180 ≦ 250
> 250 ≦ 315
> 315 ≦ 400
> 400		 + 0 to – 0.070
+ 0 to – 0.085
+ 0 to – 0.100
+ 0 to – 0.120
+ 0 to – 0.140
+ 0 to – 0.160
+ 0 to – 0.185
+ 0 to – 0.210
+ 0 to – 0.230
+ 0 to – 0.250

3. Precision Round Steel Bar Tolerances (BS 970-3)

Tolerances for Precision Steel Bars
Section Size,
diameter		 Permitted overall variation
Class A Class B Class C
mm mm mm mm
Round ≧ 6 <75 0.05 0.025 0.013

4. Bright Round Steel Bar Tolerance (BS EN ISO 286-2 )

Round Steel Bar Tolerance ISO “H” Series in MM
NOMINAL SIZE h5 h6 h7 h8 h9 h10 h11 h12
DIAMETER mm
~ to 3 +0.004/0 +0.006/0 +0.01/0 +0.014/0 +0.025/0 +0.04/0 +0.06/0 +0.1/0
over 3 to 6 +0.005/0 +0.008/0 +0.012/0 +0.018/0 +0.03/0 +0.048/0 +0.075/0 +0.12/0
over 6 to 10 +0.006/0 +0.009/0 +0.015/0 +0.022/0 +0.036/0 +0.058/0 +0.09/0 +0.15/0
over 10 to 18 +0.008/0 +0.011/0 +0.018/0 +0.027/0 +0.043/0 +0.07/0 +0.11/0 +0.18/0
over 18 to 30 +0.009/0 +0.013/0 +0.021/0 +0.033/0 +0.052/0 +0.084/0 +0.13/0 +0.21/0
over 30 to 50 +0.011/0 +0.016/0 +0.025/0 +0.039/0 +0.062/0 +0.1/0 +0.16/0 +0.25/0
over 50 to 80 +0.013/0 +0.019/0 +0.03/0 +0.046/0 +0.074/0 +0.12/0 +0.19/0 +0.3/0
over 80 to 120 +0.015/0 +0.022/0 +0.035/0 +0.054/0 +0.087/0 +0.14/0 +0.22/0 +0.35/0
over 120 to 180 +0.018/0 +0.025/0 +0.04/0 +0.063/0 +0.1/0 +0.16/0 +0.25/0 +0.4/0
over 180 to 250 +0.02/0 +0.029/0 +0.046/0 +0.072/0 +0.115/0 +0.185/0 +0.29/0 +0.46/0

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