When selecting structural steel tubing for construction or industrial applications, precision matters just as much as strength. ASTM A500 Grade C steel tube is widely recognized for its superior yield strength and durability, making it a top choice for structural frameworks, bridges, machinery, and more. However, beyond its mechanical properties, another critical factor must pay close attention to is dimensional tolerance. Accurate dimensions ensure proper fit, structural integrity, and compliance with international standards—helping avoid costly errors during fabrication and installation.
Outer Diameter of ASTM A500 Grade C Steel Tube
Rounds structural tubing: ±0.5%;
Square and rectangular structural tubing:
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Specified Outside Large Flat Dimension, in [mm]
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Permissible Variations Over and Under Specified Outside Flat Dimensions, in [mm]
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≤2 1/2 [65]
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0.020 [0.5]
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＞2 1/2 – ≤ 3 1/2 [＞65 – ≤90]
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0.025 [0.6]
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＞3 1/2 – ≤ 5 1/2 [＞90 – ≤140]
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0.030 [0.8]
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＞5 1/2 [140]
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0.01 times large flat dimension
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Wall Thickness of ASTM A500 Grade C Steel Tube
· Wall Thickness Tolerance: ±10% of the specified wall thickness (excluding the weld seam area).
· Welded Structural Tubing: When the internal weld bead is removed, the wall thickness at the weld location must be at least 90% of the specified value.
· Square and Rectangular Tubing: Wall thickness tolerance is measured only at the center of the flat sides.
Length of ASTM A500 Grade C Steel Tube
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Length
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≤22 ft [6.5 m]
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＞22 ft [6.5 m]
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Tolerances
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-1/4 in. – +1/2 in. [-6 mm – +13 mm]
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-1/4 in. – +3/4 in. [-6 mm – +19 mm]
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Straightness of ASTM A500 Grade C Steel Tube
Structural tubing must meet straightness requirements, allowing a maximum deviation of 1/8 inch per 5 feet of length (equivalent to 10 mm per meter).
Squareness of Sides of ASTM A500 Grade C Steel Tube
For square and rectangular tubing, adjacent sides must maintain a 90° angle, with a maximum allowable deviation of ±2°.
Corner Radius of ASTM A500 Grade C Steel Tube
In square and rectangular tubing, the radius of each outside corner should not exceed three times the specified wall thickness.
Twist of ASTM A500 Grade C Steel Tube
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Specified Otuside Large Flat Dimension, in [mm]
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Maximum Permissible Variations in Twist per 3 ft of length [Twist per Meter of Length], in [mm]
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≥1 1/2 [40]
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0.050 [1.3]
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＞1 1/2 – ≤ 2 1/2 [＞40 – ≤65]
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0.062 [1.6]
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＞2 1/2 – ≤ 4 [＞65 – ≤100]
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0.075 [1.9]
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＞4 – ≤ 6 [＞100 – ≤150]
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0.087 [2.2]
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＞6 – ≤ 8 [＞150 – ≤200]
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0.100 [2.5]
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＞8 [200]
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0.112 [2.8]
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For more: What is the density of ASTM A500 grade C round structural pipe?
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