Half-Round Profile Wire

Half-round wire is the simplest asymmetric section there is: a semicircle on a flat back. It exists because two jobs need two different faces on the same piece of metal — one face slides, seals or is seen, the other sits flat, welds or clamps. Once you have that split, the section writes itself, and it replaces a milled radius in one drawing pass.

What it is used for

Edge trim and ornament. A rounded edge that will not cut, welded or bonded along a flat strip. The flat back is the joint face; the radius is what the hand or the eye meets.

Sliding guides. The curved face runs against a track or a mating part, the flat back is clamped. Because the radius is drawn, not machined, it is constant along the whole length — which is exactly what a guide needs.

Wear strips and weld-on rails. A flat back takes a continuous weld or a structural adhesive far better than a round section does. Half-round gives you the weld face and the running face in one part.

Switches, sensors and small mechanisms. A rounded actuator face that cannot catch on a finger or a membrane, with a flat face for mounting.

The one dimension that decides everything

Half-round is specified by flat width, with the radius following: a true half-round has a radius equal to half the flat width. That is the definition, and it is also the trap — a section described as “half-round 4 mm” could mean 4 mm flat width (radius 2 mm) or 4 mm radius (8 mm flat width). A factor of two in the wrong direction. Always give both, or give the drawing.

Two common variants exist and both are quotable:

• True half-round: radius = half the flat width, a perfect semicircle.
• Shallow arc: a flatter radius than the width implies, for trim where a low profile matters more than a full round.

Tolerance normally sits on the flat width and on the height; the arc itself is a shape, not a dimension you inspect point by point. If the radius is functional — a seal or a runner — mark it and say what it bears against, and the tolerance moves there. Precision shaped wire explains how to place that callout.

Compared with round wire and with round-edge

Round wire is symmetric: it rotates in service and offers no flat face for welding or clamping. Half-round is what round wire becomes when you need orientation.

Round-edge profile wire is different again: a rectangular section with the corners broken, used where a flat face dominates and only the edges need softening. Half-round is mostly arc; round-edge is mostly flat. The boundary case — a shallow arc on a wide flat — is where buyers hesitate, and the drawing settles it. The round-edge family is on the round-edge profile wire page.

How it is drawn

Half-round sections are drawn through a shaped die from round wire, usually in a small number of passes because the reduction is uneven: the flat side gets full reduction while the arc side gets almost none. That imbalance is the manufacturing difficulty — the wire wants to curl toward the flat. Straightening and tension control handle it, and it is why a very shallow arc in a wide width can be trickier than a true half-round of the same size.

Specifications

The section sits in the profile wire sections catalogue alongside flat, square and trapezoid. If your part currently starts as a milled radius, profile wire vs shaped wire explains which supplier conversation you are actually having. Send the flat width, the height and what the arc runs against for a quote.