diff --git a/OpenNest.Core/Geometry/KeepOutOverlap.cs b/OpenNest.Core/Geometry/KeepOutOverlap.cs
new file mode 100644
index 0000000..54ecce8
--- /dev/null
+++ b/OpenNest.Core/Geometry/KeepOutOverlap.cs
@@ -0,0 +1,114 @@
+using System.Collections.Generic;
+
+namespace OpenNest.Geometry;
+
+/// <summary>
+/// Tolerance-free test of material against an axis-aligned keep-out rectangle, for
+/// rectangles too small for the tolerance-based overlap machinery (validation offsets,
+/// Clipper grids, triangulation and vector equality work at 1e-3 to 1e-5 scale and collapse
+/// such a rectangle, PM 6859db53). Positive-area overlap only: flush contact is clear, as
+/// everywhere else.
+/// </summary>
+public static class KeepOutOverlap
+{
+    /// <summary>The scale below which tolerance-based overlap tests are not trusted for a
+    /// keep-out rectangle (the validation outline chord tolerance).</summary>
+    public const double ToleranceFreeBelow = 0.001;
+
+    /// <summary>A keep-out narrower than <see cref="ToleranceFreeBelow"/> on either axis.</summary>
+    public static bool NeedsToleranceFreeTest(Box keepOut) =>
+        keepOut.Length < ToleranceFreeBelow || keepOut.Width < ToleranceFreeBelow;
+
+    /// <summary>
+    /// True when the material (perimeter minus holes) shares positive area with the open
+    /// rectangle: some boundary edge runs through its interior, or its interior lies wholly
+    /// inside the material (tested at its centre).
+    /// </summary>
+    public static bool MaterialEnters(Polygon perimeter, IReadOnlyList<Polygon> holes, Box box)
+    {
+        if (RingEnters(perimeter, box))
+            return true;
+        if (holes != null)
+            foreach (var hole in holes)
+                if (RingEnters(hole, box))
+                    return true;
+
+        var centre = new Vector((box.Left + box.Right) / 2, (box.Bottom + box.Top) / 2);
+        if (!Contains(perimeter, centre))
+            return false;
+        if (holes != null)
+            foreach (var hole in holes)
+                if (Contains(hole, centre))
+                    return false;
+        return true;
+    }
+
+    private static bool RingEnters(Polygon ring, Box box)
+    {
+        var vertices = ring.Vertices;
+        var count = vertices.Count;
+        for (var i = 0; i < count; i++)
+        {
+            var next = vertices[(i + 1) % count];
+            if (SegmentEntersOpenBox(vertices[i], next, box))
+                return true;
+        }
+        return false;
+    }
+
+    /// <summary>Liang-Barsky clip against the open rectangle; a positive-length part of the
+    /// segment must lie strictly inside it.</summary>
+    private static bool SegmentEntersOpenBox(Vector p, Vector q, Box box)
+    {
+        var dx = q.X - p.X;
+        var dy = q.Y - p.Y;
+        var t0 = 0.0;
+        var t1 = 1.0;
+        return Clip(-dx, p.X - box.Left, ref t0, ref t1)
+            && Clip(dx, box.Right - p.X, ref t0, ref t1)
+            && Clip(-dy, p.Y - box.Bottom, ref t0, ref t1)
+            && Clip(dy, box.Top - p.Y, ref t0, ref t1)
+            && t0 < t1;
+    }
+
+    /// <summary>Restricts [t0, t1] to the parameters where <c>denominator * t &lt; numerator</c>.</summary>
+    private static bool Clip(double denominator, double numerator, ref double t0, ref double t1)
+    {
+        if (denominator == 0)
+            return numerator > 0;
+        var r = numerator / denominator;
+        if (denominator < 0)
+        {
+            if (r >= t1)
+                return false;
+            if (r > t0)
+                t0 = r;
+        }
+        else
+        {
+            if (r <= t0)
+                return false;
+            if (r < t1)
+                t1 = r;
+        }
+        return true;
+    }
+
+    /// <summary>Even-odd ray cast; exact for a point that is not on the ring (callers only
+    /// ask after ruling out any edge through the rectangle containing the point).</summary>
+    private static bool Contains(Polygon ring, Vector point)
+    {
+        var inside = false;
+        var vertices = ring.Vertices;
+        var count = vertices.Count;
+        for (int i = 0, j = count - 1; i < count; j = i++)
+        {
+            var a = vertices[i];
+            var b = vertices[j];
+            if ((a.Y > point.Y) != (b.Y > point.Y)
+                && point.X < (b.X - a.X) * (point.Y - a.Y) / (b.Y - a.Y) + a.X)
+                inside = !inside;
+        }
+        return inside;
+    }
+}
diff --git a/OpenNest.Engine.Tests/Jobs/TinyClampZoneTests.cs b/OpenNest.Engine.Tests/Jobs/TinyClampZoneTests.cs
new file mode 100644
index 0000000..681ead2
--- /dev/null
+++ b/OpenNest.Engine.Tests/Jobs/TinyClampZoneTests.cs
@@ -0,0 +1,134 @@
+using OpenNest.CNC;
+using OpenNest.Engine.Jobs;
+using OpenNest.Engine.NestingEngines.Default;
+using OpenNest.Engine.NestingEngines.Rectangles;
+using OpenNest.Geometry;
+
+namespace OpenNest.Engine.Tests.Jobs;
+
+/// <summary>
+/// C16 (PM 6859db53): a clamp zone the job validator accepts may be far smaller than the
+/// validation outline tolerance (here 1e-5 square). Every keep-out consumer must check it
+/// without throwing, flag a placement whose material overlaps it (plus the D6 clearance),
+/// and keep a placement that only touches or clears it clear. Tolerances are unchanged (C5):
+/// the expected verdicts below are exact rectangle arithmetic, not the checker's output.
+/// </summary>
+public class TinyClampZoneTests
+{
+    private const double Tiny = 1e-5;
+
+    private static readonly ClampZone TinyZone = new("tiny", new Box(8, 0, Tiny, Tiny));
+
+    private static Program SquareProgram()
+    {
+        var program = new Program();
+        program.Codes.Add(new RapidMove(0, 0));
+        program.Codes.Add(new LinearMove(2, 0));
+        program.Codes.Add(new LinearMove(2, 2));
+        program.Codes.Add(new LinearMove(0, 2));
+        program.Codes.Add(new LinearMove(0, 0));
+        return program;
+    }
+
+    private static NestJobPart Square() =>
+        new("square", PartGeometrySnapshot.FromProgram(SquareProgram()), 1, 0, RotationPolicy.Fixed(0));
+
+    private static NestPlateStock Stock(double bottom) =>
+        new("sheet", new Size(10, 12), null, 0, new Spacing(0, bottom, 0, 0), 1,
+            new[] { TinyZone });
+
+    private static NestJob Job(double bottom) => new(new[] { Square() }, new[] { Stock(bottom) });
+
+    private static IReadOnlyList<string> ClampViolations(NestJob job, NestJobResult result) =>
+        NestLayoutCheck.Violations(job, result).Where(v => v.Contains("clamp zone")).ToList();
+
+    [Fact]
+    public void RectanglesResultOnATinyClampIsCheckedWithoutThrowing()
+    {
+        // The PM probe: Rectangles places the square flush against the tiny clamp.
+        var job = Job(0);
+        NestJobValidator.Validate(job);
+        var result = new RectanglesNestingEngine().Solve(job);
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+
+        var violations = ClampViolations(job, result);
+
+        // Independent oracle: the square's footprint shares no positive area with the zone.
+        var pose = Assert.Single(result.Plates.SelectMany(p => p.Placements));
+        var overlapX = System.Math.Min(pose.X + 2, 8 + Tiny) - System.Math.Max(pose.X, 8);
+        var overlapY = System.Math.Min(pose.Y + 2, Tiny) - System.Math.Max(pose.Y, 0);
+        var expectOverlap = overlapX > 0 && overlapY > 0;
+        Assert.Equal(expectOverlap, violations.Count > 0);
+    }
+
+    [Fact]
+    public void DefaultSolvesATinyClampJobToAValidResult()
+    {
+        var job = Job(0);
+        var result = new DefaultNestingEngine().Solve(job);
+        Assert.Equal(NestJobStatus.Complete, result.Status);
+        Assert.Empty(NestLayoutCheck.Violations(job, result));
+    }
+
+    // (bottom edge spacing, x, y, material overlaps the zone inflated by the clearance).
+    // The keep-out is [8 - c, 8 + 1e-5 + c] x [-c, 1e-5 + c] with c = bottom - 0.0005
+    // (the shared spacing slack); the 2x2 square spans [x, x+2] x [y, y+2].
+    [Theory]
+    [InlineData(0.0, 7.5, 0.0, true)]       // covers the zone
+    [InlineData(0.0, 6.0, 0.0, false)]      // right edge flush on the zone's left side
+    [InlineData(0.0, 8.00001, 0.0, false)]  // left edge flush on the zone's right side
+    [InlineData(0.0, 8.0, Tiny, false)]     // bottom edge flush on the zone's top
+    [InlineData(0.0, 3.0, 0.0, false)]      // well clear
+    [InlineData(0.25, 7.5, 0.1, true)]      // over the zone, inside the clearance band
+    [InlineData(0.25, 8.0, 0.24, true)]     // above the zone but inside the clearance
+    [InlineData(0.25, 8.25001, 0.1, false)] // exactly at the clearance to the right
+    [InlineData(0.25, 7.0, 0.25001, false)] // exactly at the clearance above
+    [InlineData(0.25, 3.0, 0.25, false)]    // well clear
+    public void LayoutCheckJudgesPlacementsAgainstATinyClamp(double bottom, double x, double y,
+        bool overlaps)
+    {
+        var job = Job(bottom);
+        NestJobValidator.Validate(job);
+        var stock = job.Plates[0];
+        var result = new NestJobResult(NestJobStatus.Complete, NestJobStopReason.Completed,
+            new[] { new NestJobPlateResult(0, stock, new[] { new NestJobPlacement("square", 0, x, y, 0) }) },
+            Array.Empty<PartFulfillment>(), Array.Empty<StockUsage>());
+
+        var violations = ClampViolations(job, result);
+
+        Assert.Equal(overlaps, violations.Count > 0);
+    }
+
+    private static Program FrameProgram()
+    {
+        // 4x4 square with a 2x2 hole in its middle.
+        var program = new Program();
+        program.Codes.Add(new RapidMove(0, 0));
+        program.Codes.Add(new LinearMove(4, 0));
+        program.Codes.Add(new LinearMove(4, 4));
+        program.Codes.Add(new LinearMove(0, 4));
+        program.Codes.Add(new LinearMove(0, 0));
+        program.Codes.Add(new RapidMove(1, 1));
+        program.Codes.Add(new LinearMove(1, 3));
+        program.Codes.Add(new LinearMove(3, 3));
+        program.Codes.Add(new LinearMove(3, 1));
+        program.Codes.Add(new LinearMove(1, 1));
+        return program;
+    }
+
+    // The tiny zone inside the frame's hole is clear; inside its material it is not.
+    [Theory]
+    [InlineData(6.0, -2.0, false)] // hole spans [7, 9] x [-1, 1] around the zone
+    [InlineData(6.0, 0.0, true)]   // the frame's bottom bar covers the zone
+    public void LayoutCheckSeesHolesAroundATinyClamp(double x, double y, bool overlaps)
+    {
+        var frame = new NestJobPart("frame", PartGeometrySnapshot.FromProgram(FrameProgram()), 1, 0,
+            RotationPolicy.Fixed(0));
+        var job = new NestJob(new[] { frame }, new[] { Stock(0) });
+        var result = new NestJobResult(NestJobStatus.Complete, NestJobStopReason.Completed,
+            new[] { new NestJobPlateResult(0, job.Plates[0], new[] { new NestJobPlacement("frame", 0, x, y, 0) }) },
+            Array.Empty<PartFulfillment>(), Array.Empty<StockUsage>());
+
+        Assert.Equal(overlaps, ClampViolations(job, result).Count > 0);
+    }
+}
diff --git a/OpenNest.Engine/Jobs/NestLayoutCheck.cs b/OpenNest.Engine/Jobs/NestLayoutCheck.cs
index dbad50a..5bd6ddd 100644
--- a/OpenNest.Engine/Jobs/NestLayoutCheck.cs
+++ b/OpenNest.Engine/Jobs/NestLayoutCheck.cs
@@ -187,7 +187,7 @@ public static class NestLayoutCheck
                     continue;
 
                 var material = Outline(part, 0);
-                if (material == null || !Overlaps(material, keepOutOutline))
+                if (material == null || !OverlapsKeepOut(material, keepOutOutline, keepOut))
                     continue;
 
                 result.Add(
@@ -198,17 +198,33 @@ public static class NestLayoutCheck
         }
     }
 
+    /// <summary>
+    /// The keep-out as an exact four-vertex ring. Routing a synthetic rectangle through the
+    /// tolerance-based validation offset collapses a zone smaller than that tolerance to
+    /// nothing (PM 6859db53), so the rectangle is never offset or flattened here.
+    /// </summary>
     private static PartOutline RectangleOutline(Box box)
     {
-        var ring = new List<Geometry.Entity>
-        {
-            new Line(box.Left, box.Bottom, box.Right, box.Bottom),
-            new Line(box.Right, box.Bottom, box.Right, box.Top),
-            new Line(box.Right, box.Top, box.Left, box.Top),
-            new Line(box.Left, box.Top, box.Left, box.Bottom),
-        };
-        var profile = new ShapeProfile(ring);
-        return Outline(profile, new Vector(0, 0), 0);
+        var perimeter = new Polygon();
+        perimeter.Vertices.Add(new Vector(box.Left, box.Bottom));
+        perimeter.Vertices.Add(new Vector(box.Right, box.Bottom));
+        perimeter.Vertices.Add(new Vector(box.Right, box.Top));
+        perimeter.Vertices.Add(new Vector(box.Left, box.Top));
+        perimeter.Vertices.Add(new Vector(box.Left, box.Bottom));
+        perimeter.UpdateBounds();
+        return new PartOutline { Perimeter = perimeter, Holes = new List<Polygon>() };
+    }
+
+    /// <summary>
+    /// Material against a keep-out rectangle. A rectangle below the outline tolerance, or one
+    /// the triangulated test cannot prepare, is judged by the tolerance-free rectangle test
+    /// instead: the tolerant path would call real overlap clear.
+    /// </summary>
+    private static bool OverlapsKeepOut(PartOutline material, PartOutline keepOutOutline, Box keepOut)
+    {
+        if (KeepOutOverlap.NeedsToleranceFreeTest(keepOut) || keepOutOutline.Triangles == null)
+            return KeepOutOverlap.MaterialEnters(material.Perimeter, material.Holes, keepOut);
+        return Overlaps(material, keepOutOutline);
     }
 
     /// <summary>