diff --git a/OpenNest.Core/Splitting/SplitLine.cs b/OpenNest.Core/Splitting/SplitLine.cs
new file mode 100644
index 0000000..0ef4ec3
--- /dev/null
+++ b/OpenNest.Core/Splitting/SplitLine.cs
@@ -0,0 +1,17 @@
+namespace OpenNest;
+
+/// <summary>
+/// Defines a split line at a position along an axis.
+/// For Vertical, Position is the X coordinate. For Horizontal, Position is the Y coordinate.
+/// </summary>
+public class SplitLine
+{
+    public double Position { get; }
+    public CutOffAxis Axis { get; }
+
+    public SplitLine(double position, CutOffAxis axis)
+    {
+        Position = position;
+        Axis = axis;
+    }
+}
diff --git a/OpenNest.Core/Splitting/SplitParameters.cs b/OpenNest.Core/Splitting/SplitParameters.cs
new file mode 100644
index 0000000..d2f25b6
--- /dev/null
+++ b/OpenNest.Core/Splitting/SplitParameters.cs
@@ -0,0 +1,33 @@
+namespace OpenNest;
+
+public enum SplitType
+{
+    Straight,
+    WeldGapTabs,
+    SpikeGroove
+}
+
+public class SplitParameters
+{
+    public SplitType Type { get; set; } = SplitType.Straight;
+
+    // Tab parameters
+    public double TabWidth { get; set; } = 1.0;
+    public double TabHeight { get; set; } = 0.125;
+    public int TabCount { get; set; } = 3;
+
+    // Spike/Groove parameters
+    public double SpikeDepth { get; set; } = 0.5;
+    public double SpikeAngle { get; set; } = 60.0; // degrees
+    public int SpikePairCount { get; set; } = 2;
+
+    /// <summary>
+    /// Max protrusion from the split edge (for auto-fit plate size calculation).
+    /// </summary>
+    public double FeatureOverhang => Type switch
+    {
+        SplitType.WeldGapTabs => TabHeight,
+        SplitType.SpikeGroove => SpikeDepth,
+        _ => 0
+    };
+}
diff --git a/OpenNest.Tests/Splitting/SplitLineTests.cs b/OpenNest.Tests/Splitting/SplitLineTests.cs
new file mode 100644
index 0000000..1abb55e
--- /dev/null
+++ b/OpenNest.Tests/Splitting/SplitLineTests.cs
@@ -0,0 +1,31 @@
+namespace OpenNest.Tests.Splitting;
+
+public class SplitLineTests
+{
+    [Fact]
+    public void SplitLine_Vertical_StoresPositionAsX()
+    {
+        var line = new SplitLine(50.0, CutOffAxis.Vertical);
+        Assert.Equal(50.0, line.Position);
+        Assert.Equal(CutOffAxis.Vertical, line.Axis);
+    }
+
+    [Fact]
+    public void SplitLine_Horizontal_StoresPositionAsY()
+    {
+        var line = new SplitLine(30.0, CutOffAxis.Horizontal);
+        Assert.Equal(30.0, line.Position);
+        Assert.Equal(CutOffAxis.Horizontal, line.Axis);
+    }
+
+    [Fact]
+    public void SplitParameters_Defaults()
+    {
+        var p = new SplitParameters();
+        Assert.Equal(SplitType.Straight, p.Type);
+        Assert.Equal(3, p.TabCount);
+        Assert.Equal(1.0, p.TabWidth);
+        Assert.Equal(0.125, p.TabHeight);
+        Assert.Equal(2, p.SpikePairCount);
+    }
+}