Square bar stock

Square bar stock is solid material with a nominally square cross-section. It provides four longitudinal faces for parts that retain flats or are machined from a rectangular envelope. The shape does not identify the alloy, heat treatment or acceptance limits. It must also be distinguished from square hollow section, which has an internal opening and different section properties.

Corner form is part of the product identity. Nucor offers cold-finished squares with a sharp corner or a specified radius; Ovako describes hot-rolled round-corner square bar for applications including forging. Neither description should be silently substituted for the other where a component needs full corner material. Nucor cold-finished bar, Ovako square steel bar

Describe the section completely

A sharp-corner 20 mm square needs an ideal circular envelope of 20√2 = 28.284 mm. It cannot pass through a nominal 20 mm round opening in that geometry. Specify corner profile, actual across-flats size, twist and straightness before qualifying feeder clearance.

State the nominal side or width across opposite flats, the applicable limits and the required corner treatment. A drawing saying only “20 square” leaves several questions unresolved: units, surface condition, corner radius, length and whether supplied faces remain on the finished component.

These are separate characteristics. Two acceptable width measurements do not prove that the four faces are perpendicular or that their orientation remains constant along a long bar. For a close-fitting insert or guided sliding component, define the functional envelope and inspect against the actual drawing rather than inferring fit from nominal side alone.

Material, route and applicable standards

Keep the material specification and supplied condition alongside the dimensional description. ASTM A108-24 covers cold-finished carbon and alloy steel bars, in straight lengths and coils, for purposes including machining and as-finished applications. Its supplementary requirements apply only when individually ordered. It is not the specification for every stainless, copper-alloy or aluminum square sold by a stockist. ASTM A108-24 scope

For hot-rolled square steel bars for general purposes, EN 10059:2003 concerns dimensions and tolerances on shape and dimensions. DIN's current catalog identifies its national adoption as DIN EN 10059:2004-02. That dimensional-standard title is not a steel-grade designation or a guarantee of finished-part strength. Preserve the ordered material standard and grade separately. DIN EN 10059 record

Nucor's cold-finished square offering lists several carbon and alloy grades across an overall 7/16–5 inch size range, depending on grade. The range does not establish availability of every grade at every size. Its tolerance guidance also depends on shape, carbon content and finishing method; obtain the actual table applicable to the requested product. Nucor squares and tolerance guidance

A bounded supplier example

Atlas's 1045 data sheet revised 10 September 2021 states h11 tolerance for its square, hexagonal and flat bar. It separately lists a maximum straightness deviation of 1 mm in 375 mm for these shapes. Those entries concern that supplier's stated product and edition; they do not define universal square-bar tolerances, squareness, twist or the corner profile. Obtain the numerical size limits for the ordered section and confirm any additional geometric requirements. Atlas 1045, p. 2

The same sheet explicitly distinguishes ordinary chemical-composition-based supply from specially ordered guaranteed mechanical properties. Its typical-property information is not evidence that every piece marked 1045 satisfies a chosen strength minimum. A shape name and grade number together still do not replace the purchase specification and certificate. Atlas 1045, p. 1

Original geometry example

Assume an ideal sharp-cornered square of side a, with straight, parallel faces. Its area is a², diagonal is a√2, and volume for length L is a²L.

For 20.000 mm square × 1,000 mm long:

• Section area is 20² = 400.000 mm².
• Across-corner diagonal is 20√2 = 28.284 mm.
• Volume is 400 × 1000 = 400,000 mm³ = 0.400 L.

A circular passage of nominal diameter 20 mm cannot admit that sharp-cornered 20 mm square. Its ideal corner envelope requires 28.284 mm before any clearance or tolerance allowance. Conversely, a nominal 20 mm diameter circle fits inside the ideal square. Turning that circle retains (π × 20² / 4) / 400 = 78.54% of the starting section and removes 21.46%, before facing or other features.

Corner radii change the result. For an ideal rounded square with overall width a and four identical tangent quarter-circle corner radii r, area is a² − (4 − π)r². Keeping a at 20 mm and assuming r = 2 mm gives 396.566 mm², about 0.86% less area than the sharp square. This is an illustrative profile, not a supplier's corner allowance or a section-property table.

Match the stock to the next operation

Ovako identifies its round-corner square bar as a forging-oriented product, describing the avoidance of sharp edges that can contribute to laps or surface defects during forging. This is a reason to distinguish feedstock profiles, not a universal forging qualification or permission to remove a finished component's required corners. Establish the appropriate grade, heating and forming process for the actual component. Ovako round-corner square-bar description

For machined parts, work backward from retained faces, corners and datums. Allocate cleanup stock for permitted size/form variation and surface condition; define whether faces will be milled or used as supplied. Confirm end preparation and usable length rather than treating a mill-length bar as a finished cut blank. Nucor lists several available end treatments, including sawcut and chamfered ends, which must be resolved in the order. Nucor end-condition guidance

A practical receiving record should connect material/condition, complete geometry, inspection results and heat/lot identity. Keep identity through cutting and machining. Qualify the workholding and process against the actual stock; the square-bar label supplies no general load rating, welding procedure, machining speed or finished-fit guarantee.

Source versions and related reference

Reviewed 2026-11-01, America/Los_Angeles. ASTM identifies A108-24; DIN identifies the February 2004 adoption of EN 10059:2003. Atlas prints revision and print date 10 September 2021. Nucor and Ovako's cited live pages have no explicit technical revision date. Confirm contractual editions and current supply provisions when ordering. Geometry examples are original calculations with their assumptions stated above.

Stock forms and dimensions