BS 970 (Tollerances)

SIZE millimeters

mm
deviation

mm
 
Width

Flats

< 18 ­ 0,11  
> 18     < 30 ­ 0,13  
> 30     < 50 ­ 0,16  
> 50     < 80  ­ 0,19  
> 80     < 100  ­ 0,22  
> 100   < 130  ­ 0,35  
> 130   < 160  ­ 1,00  
> 160   < 320  ­ 2,00  
 
Thickness

Flats

< 18 ­ 0,11  
> 18     < 30 ­ 0,13  
> 30     < 50 ­ 0,25  
> 50     < 80  ­ 0,35  
 
Squares > 6        < 18 ­ 0,09  
> 18     < 30 ­ 0,11  
> 30     < 50 ­ 0,13  
> 50     < 80  ­ 0,16  
> 80     < 105 ­ 0,25  
 
Hexagons > 6        < 18 ­ 0,09  
> 18     < 30 ­ 0,11  
> 30     < 50 ­ 0,13  
> 50     < 80  ­ 0,16  
> 80     < 105 ­ 0,25  
 
Rounds > 6       < 18 ­ 0,070  
> 18     < 30 ­ 0,085  
> 30     < 50 ­ 0,100  
> 50     < 80  ­ 0,120  
> 80     < 100 ­ 0,140  
 
Sise tolerances are usually specified as minus
 
Straightness Tolerances BS 970 (Pt. 3:1991) for Cold Finished Bars 
 
Section Steel grade Permitted variation mm
 
Rounds < 0,25 % carbon

> 0,25 % carbon, alloys and all heat treated grades 

1 / 1000

1 / 500

Squares
and

Hexagons
< 0,25 % carbon                < 75 mm

> 75 mm

> 0,25 % carbon, alloys and all heat treated grades   

1 / 750

1 / 500

1 / 375

Flats < 0,25 % carbon

> 0,25 % carbon, alloys and all heat treated grades 

1 / 500

1 / 375

Drawn and turned bars shall be supplied to the tolerances shall be measured as maximum deviation from straightness in any 3000 mm portion of the bar.