diff --git a/OpenNest.Data/ClampSettings.cs b/OpenNest.Data/ClampSettings.cs
new file mode 100644
index 0000000..5192019
--- /dev/null
+++ b/OpenNest.Data/ClampSettings.cs
@@ -0,0 +1,307 @@
+using System.Text.Json;
+
+namespace OpenNest.Data;
+
+/// <summary>Outcome of <see cref="ClampSettings.Load(string, out ClampSettingsStatus)"/>.</summary>
+public enum ClampSettingsStatus
+{
+    /// <summary>Every value present in the file was valid.</summary>
+    Ok,
+
+    /// <summary>No file exists at the path; clamps stay off.</summary>
+    Missing,
+
+    /// <summary>
+    /// The file loaded, but some values were invalid and were ignored (an invalid clamp
+    /// center is dropped, other fields fall back individually). Callers should warn: the
+    /// resulting rail may lack a physical clamp.
+    /// </summary>
+    Partial,
+
+    /// <summary>The file exists but could not be read or parsed; clamps stay off.</summary>
+    Invalid,
+}
+
+/// <summary>
+/// The machine's fixed edge-clamp rail, persisted to a single JSON file (by default
+/// %APPDATA%\OpenNest\clamps.json). Off by default: until <see cref="Enabled"/> is set
+/// with at least one center, new nests get no clamps and behave exactly as before.
+/// Loading never throws; values are validated field by field.
+/// </summary>
+public sealed class ClampSettings
+{
+    public const int CurrentVersion = 1;
+
+    /// <summary>Default clamp extent along the edge, in <see cref="Units"/> (inches).</summary>
+    public const double DefaultWidth = 1.5;
+
+    /// <summary>Default clamp intrusion into the sheet, in <see cref="Units"/> (inches).</summary>
+    public const double DefaultDepth = 0.625;
+
+    private const double MillimetersPerInch = 25.4;
+
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        WriteIndented = true,
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        PropertyNameCaseInsensitive = true,
+    };
+
+    /// <summary>Whether new nests receive this rail. Default off.</summary>
+    public bool Enabled { get; set; }
+
+    /// <summary>Units of <see cref="Width"/>, <see cref="Depth"/> and <see cref="Centers"/>.</summary>
+    public Units Units { get; set; } = Units.Inches;
+
+    public double Width { get; set; } = DefaultWidth;
+
+    public double Depth { get; set; } = DefaultDepth;
+
+    /// <summary>Clamp centers along X, measured from the plate origin.</summary>
+    public IReadOnlyList<double> Centers { get; set; } = Array.Empty<double>();
+
+    /// <summary>The built-in settings used for a missing or unreadable file: clamps off.</summary>
+    public static ClampSettings Fallback => new();
+
+    /// <summary>%APPDATA%\OpenNest\clamps.json.</summary>
+    public static string DefaultPath =>
+        Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+            "OpenNest",
+            "clamps.json"
+        );
+
+    /// <summary>
+    /// Captures a nest's rail (or the default clamp size and no centers when it has none)
+    /// in that nest's units, e.g. for "save as machine defaults".
+    /// </summary>
+    public static ClampSettings FromRail(ClampRail? rail, Units units, bool enabled) =>
+        new()
+        {
+            Enabled = enabled,
+            Units = units,
+            Width = rail?.Width ?? ConvertDefault(DefaultWidth, units),
+            Depth = rail?.Depth ?? ConvertDefault(DefaultDepth, units),
+            Centers = rail?.Centers.ToArray() ?? Array.Empty<double>(),
+        };
+
+    /// <summary>
+    /// The rail a new nest in <paramref name="units"/> receives, or null when clamps are
+    /// disabled or no center is configured. Values are converted between inches and
+    /// millimeters as needed.
+    /// </summary>
+    public ClampRail? RailFor(Units units)
+    {
+        if (!Enabled || Centers.Count == 0)
+            return null;
+
+        var scale = Scale(Units, units);
+        return new ClampRail(Width * scale, Depth * scale, Centers.Select(c => c * scale));
+    }
+
+    /// <summary>
+    /// Gives a newly created nest this machine rail when enabled (after the nest's units are
+    /// set); otherwise leaves it untouched.
+    /// </summary>
+    public void ApplyToNewNest(Nest nest)
+    {
+        ArgumentNullException.ThrowIfNull(nest);
+        var rail = RailFor(nest.Units);
+        if (rail != null)
+            nest.SetClampRail(rail);
+    }
+
+    public static ClampSettings Load(string path) => Load(path, out _);
+
+    /// <summary>
+    /// Loads the settings, never throwing. A missing or unreadable file yields
+    /// <see cref="Fallback"/> (clamps off); a readable file merges valid values over it and
+    /// reports <see cref="ClampSettingsStatus.Partial"/> if anything was ignored.
+    /// </summary>
+    public static ClampSettings Load(string path, out ClampSettingsStatus status)
+    {
+        var settings = Fallback;
+        if (string.IsNullOrWhiteSpace(path) || !File.Exists(path))
+        {
+            status = ClampSettingsStatus.Missing;
+            return settings;
+        }
+
+        ClampSettingsDto? dto;
+        try
+        {
+            dto = JsonSerializer.Deserialize<ClampSettingsDto>(File.ReadAllText(path), JsonOptions);
+        }
+        catch (Exception ex) when (IsUnreadableFile(ex))
+        {
+            status = ClampSettingsStatus.Invalid;
+            return settings;
+        }
+
+        if (dto is null)
+        {
+            status = ClampSettingsStatus.Invalid;
+            return settings;
+        }
+
+        var ignored = false;
+
+        if (dto.Enabled is { } enabled)
+        {
+            if (enabled.ValueKind is JsonValueKind.True or JsonValueKind.False)
+                settings.Enabled = enabled.GetBoolean();
+            else
+                ignored = true;
+        }
+
+        if (dto.Units is { } units)
+        {
+            if (TryParseUnits(units, out var parsed))
+                settings.Units = parsed;
+            else
+                ignored = true;
+        }
+
+        if (dto.Width is { } width)
+        {
+            if (TryPositive(width, out var value))
+                settings.Width = value;
+            else
+                ignored = true;
+        }
+
+        if (dto.Depth is { } depth)
+        {
+            if (TryPositive(depth, out var value))
+                settings.Depth = value;
+            else
+                ignored = true;
+        }
+
+        if (dto.Centers is { } centers)
+        {
+            if (centers.ValueKind == JsonValueKind.Array)
+            {
+                var valid = new List<double>();
+                foreach (var center in centers.EnumerateArray())
+                {
+                    if (
+                        center.ValueKind == JsonValueKind.Number
+                        && center.TryGetDouble(out var x)
+                        && double.IsFinite(x)
+                        && x >= 0
+                    )
+                        valid.Add(x);
+                    else
+                        ignored = true;
+                }
+                settings.Centers = valid.Distinct().OrderBy(x => x).ToArray();
+            }
+            else
+            {
+                ignored = true;
+            }
+        }
+
+        status = ignored ? ClampSettingsStatus.Partial : ClampSettingsStatus.Ok;
+        return settings;
+    }
+
+    /// <summary>
+    /// Writes the file (creating the parent directory), retrying briefly on IO collisions
+    /// the same way <see cref="LocalJsonProvider"/> does.
+    /// </summary>
+    public void Save(string path, int maxRetries = 3)
+    {
+        var dto = new
+        {
+            version = CurrentVersion,
+            enabled = Enabled,
+            units = Units.ToString().ToLowerInvariant(),
+            width = Width,
+            depth = Depth,
+            centers = Centers,
+        };
+        var json = JsonSerializer.Serialize(dto, JsonOptions);
+
+        var directory = Path.GetDirectoryName(Path.GetFullPath(path));
+        if (!string.IsNullOrEmpty(directory))
+            Directory.CreateDirectory(directory);
+
+        for (var attempt = 0; attempt < maxRetries; attempt++)
+        {
+            try
+            {
+                File.WriteAllText(path, json);
+                return;
+            }
+            catch (IOException) when (attempt < maxRetries - 1)
+            {
+                Thread.Sleep(100);
+            }
+        }
+    }
+
+    private static double Scale(Units from, Units to) =>
+        from == to ? 1
+        : from == Units.Inches ? MillimetersPerInch
+        : 1 / MillimetersPerInch;
+
+    private static double ConvertDefault(double inches, Units units) =>
+        inches * Scale(Units.Inches, units);
+
+    private static bool TryPositive(JsonElement element, out double value)
+    {
+        value = 0;
+        return element.ValueKind == JsonValueKind.Number
+            && element.TryGetDouble(out value)
+            && double.IsFinite(value)
+            && value > 0;
+    }
+
+    /// <summary>
+    /// Accepts only a defined unit name (case-insensitive); Enum.TryParse would also accept
+    /// numeric strings and comma-joined names.
+    /// </summary>
+    private static bool TryParseUnits(JsonElement element, out Units units)
+    {
+        units = default;
+        if (element.ValueKind != JsonValueKind.String)
+            return false;
+
+        var text = element.GetString();
+        foreach (var candidate in Enum.GetValues<Units>())
+        {
+            if (string.Equals(candidate.ToString(), text, StringComparison.OrdinalIgnoreCase))
+            {
+                units = candidate;
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private static bool IsUnreadableFile(Exception ex) =>
+        ex
+            is JsonException
+                or IOException
+                or UnauthorizedAccessException
+                or NotSupportedException
+                or System.Security.SecurityException;
+
+    /// <summary>
+    /// Wire format. Every value is read as raw JSON so a wrongly typed field falls back on
+    /// its own instead of failing the whole file; unknown fields (including a future higher
+    /// <c>version</c>) are ignored.
+    /// </summary>
+    private sealed record ClampSettingsDto
+    {
+        public JsonElement? Version { get; init; }
+        public JsonElement? Enabled { get; init; }
+        public JsonElement? Units { get; init; }
+        public JsonElement? Width { get; init; }
+        public JsonElement? Depth { get; init; }
+        public JsonElement? Centers { get; init; }
+    }
+}
diff --git a/OpenNest.Tests/Data/ClampSettingsTests.cs b/OpenNest.Tests/Data/ClampSettingsTests.cs
new file mode 100644
index 0000000..c90bf30
--- /dev/null
+++ b/OpenNest.Tests/Data/ClampSettingsTests.cs
@@ -0,0 +1,285 @@
+using System.Text.Json;
+using OpenNest.Data;
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.Data;
+
+/// <summary>
+/// The machine clamp settings store (%APPDATA%\OpenNest\clamps.json): off by default, a
+/// never-throwing read that degrades value by value, and no effect until enabled.
+/// </summary>
+public class ClampSettingsTests : IDisposable
+{
+    private static readonly double[] MachineCenters = { 6, 21, 36, 51, 66, 81, 96, 111 };
+
+    private readonly string _directory = Path.Combine(
+        Path.GetTempPath(), "OpenNestTests", Guid.NewGuid().ToString());
+    private readonly string _path;
+
+    public ClampSettingsTests()
+    {
+        Directory.CreateDirectory(_directory);
+        _path = Path.Combine(_directory, "clamps.json");
+    }
+
+    public void Dispose()
+    {
+        if (!Directory.Exists(_directory))
+            return;
+        if (!OperatingSystem.IsWindows() && File.Exists(_path))
+            File.SetUnixFileMode(_path, UnixFileMode.UserRead | UnixFileMode.UserWrite);
+        Directory.Delete(_directory, recursive: true);
+    }
+
+    private static ClampSettings Machine(bool enabled = true) => new()
+    {
+        Enabled = enabled,
+        Width = 1.5,
+        Depth = 0.625,
+        Centers = MachineCenters,
+    };
+
+    private static void AssertFallback(ClampSettings settings)
+    {
+        Assert.False(settings.Enabled);
+        Assert.Equal(Units.Inches, settings.Units);
+        Assert.Equal(1.5, settings.Width);
+        Assert.Equal(0.625, settings.Depth);
+        Assert.Empty(settings.Centers);
+        Assert.Null(settings.RailFor(Units.Inches));
+    }
+
+    [Fact]
+    public void DefaultPathUsesTheApplicationDataOpenNestDirectory()
+    {
+        Assert.Equal(
+            Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+                "OpenNest", "clamps.json"),
+            ClampSettings.DefaultPath);
+    }
+
+    [Fact]
+    public void MissingFileKeepsClampsOff()
+    {
+        var loaded = ClampSettings.Load(_path, out var status);
+
+        Assert.Equal(ClampSettingsStatus.Missing, status);
+        AssertFallback(loaded);
+        Assert.Equal(ClampSettingsStatus.Missing, LoadStatus(""));
+    }
+
+    [Fact]
+    public void SaveThenLoadRoundTripsAsCamelCaseJson()
+    {
+        Machine().Save(_path);
+
+        var loaded = ClampSettings.Load(_path, out var status);
+        using var json = JsonDocument.Parse(File.ReadAllText(_path));
+
+        Assert.Equal(ClampSettingsStatus.Ok, status);
+        Assert.True(loaded.Enabled);
+        Assert.Equal(Units.Inches, loaded.Units);
+        Assert.Equal(1.5, loaded.Width);
+        Assert.Equal(0.625, loaded.Depth);
+        Assert.Equal(MachineCenters, loaded.Centers);
+        var root = json.RootElement;
+        Assert.Equal(1, root.GetProperty("version").GetInt32());
+        Assert.True(root.GetProperty("enabled").GetBoolean());
+        Assert.Equal("inches", root.GetProperty("units").GetString());
+        Assert.Equal(8, root.GetProperty("centers").GetArrayLength());
+    }
+
+    [Fact]
+    public void SaveCreatesTheSettingsDirectory()
+    {
+        var nested = Path.Combine(_directory, "AppData", "OpenNest", "clamps.json");
+
+        Machine().Save(nested);
+
+        Assert.True(ClampSettings.Load(nested).Enabled);
+    }
+
+    [Fact]
+    public void NothingChangesUntilEnabled()
+    {
+        var nest = new Nest();
+        Machine(enabled: false).ApplyToNewNest(nest);
+
+        Assert.Null(Machine(enabled: false).RailFor(Units.Inches));
+        Assert.Null(nest.PlateDefaults.ClampRail);
+        Assert.Empty(nest.CreatePlate().ClampZones);
+
+        // Enabled without any clamp center is still no clamps.
+        var empty = Machine();
+        empty.Centers = Array.Empty<double>();
+        Assert.Null(empty.RailFor(Units.Inches));
+    }
+
+    [Fact]
+    public void EnabledSettingsGiveANewNestTheMachineRail()
+    {
+        var nest = new Nest { Units = Units.Inches };
+        nest.PlateDefaults.Size = new Size(48, 60);
+
+        Machine().ApplyToNewNest(nest);
+        var plate = nest.CreatePlate();
+
+        Assert.Equal(new ClampRail(1.5, 0.625, MachineCenters), nest.PlateDefaults.ClampRail);
+        Assert.Equal(new[] { 5.25, 20.25, 35.25, 50.25 }, plate.ClampZones.Select(z => z.Bounds.X));
+    }
+
+    [Fact]
+    public void RailIsConvertedToTheNestsUnits()
+    {
+        var metric = Machine().RailFor(Units.Millimeters)!;
+        Assert.Equal(1.5 * 25.4, metric.Width, 12);
+        Assert.Equal(0.625 * 25.4, metric.Depth, 12);
+        Assert.Equal(6 * 25.4, metric.Centers[0], 12);
+
+        var settings = new ClampSettings
+        {
+            Enabled = true,
+            Units = Units.Millimeters,
+            Width = 38.1,
+            Depth = 15.875,
+            Centers = new[] { 152.4 },
+        };
+        var inches = settings.RailFor(Units.Inches)!;
+        Assert.Equal(1.5, inches.Width, 12);
+        Assert.Equal(6, inches.Centers[0], 12);
+        Assert.Equal(38.1, settings.RailFor(Units.Millimeters)!.Width);
+    }
+
+    [Fact]
+    public void PartialFileMergesOverTheDefaults()
+    {
+        File.WriteAllText(_path, """{ "enabled": true, "centers": [21, 6] }""");
+
+        var loaded = ClampSettings.Load(_path, out var status);
+
+        Assert.Equal(ClampSettingsStatus.Ok, status);
+        Assert.True(loaded.Enabled);
+        Assert.Equal(1.5, loaded.Width);
+        Assert.Equal(0.625, loaded.Depth);
+        Assert.Equal(new[] { 6.0, 21 }, loaded.Centers);
+    }
+
+    [Fact]
+    public void InvalidValuesFallBackIndividuallyAndAreReported()
+    {
+        File.WriteAllText(_path, """
+            {
+              "enabled": "yes",
+              "units": "7",
+              "width": -1,
+              "depth": "deep",
+              "centers": [6, "x", -3, 21, 1e400, 21],
+              "future": { "ignored": true }
+            }
+            """);
+
+        var loaded = ClampSettings.Load(_path, out var status);
+
+        Assert.Equal(ClampSettingsStatus.Partial, status);
+        Assert.False(loaded.Enabled);
+        Assert.Equal(Units.Inches, loaded.Units);
+        Assert.Equal(1.5, loaded.Width);
+        Assert.Equal(0.625, loaded.Depth);
+        Assert.Equal(new[] { 6.0, 21 }, loaded.Centers);
+    }
+
+    [Theory]
+    [InlineData("""{ "centers": 6 }""")]
+    [InlineData("""{ "centers": [6, -1] }""")]
+    [InlineData("""{ "centers": [6, "21"] }""")]
+    [InlineData("""{ "units": ["inches"] }""")]
+    [InlineData("""{ "enabled": 1 }""")]
+    [InlineData("""{ "width": 0 }""")]
+    public void AnySingleInvalidValueIsReported(string json)
+    {
+        File.WriteAllText(_path, json);
+        Assert.Equal(ClampSettingsStatus.Partial, LoadStatus(_path));
+    }
+
+    [Fact]
+    public void AnInvalidCenterIsDroppedButTheRestOfTheRailStillLoads()
+    {
+        File.WriteAllText(_path, """{ "enabled": true, "centers": [6, "21", 36] }""");
+
+        var loaded = ClampSettings.Load(_path, out var status);
+
+        // The operator must be warned: the rail is now missing a physical clamp.
+        Assert.Equal(ClampSettingsStatus.Partial, status);
+        Assert.True(loaded.Enabled);
+        Assert.Equal(new[] { 6.0, 36 }, loaded.Centers);
+    }
+
+    [Theory]
+    [InlineData("{ this is not json")]
+    [InlineData("[6, 21, 36]")]
+    [InlineData("null")]
+    [InlineData("")]
+    public void UnparseableFileKeepsClampsOffAndIsReported(string json)
+    {
+        File.WriteAllText(_path, json);
+
+        var loaded = ClampSettings.Load(_path, out var status);
+
+        Assert.Equal(ClampSettingsStatus.Invalid, status);
+        AssertFallback(loaded);
+    }
+
+    [SkippableFact]
+    public void UnreadableFileKeepsClampsOffAndIsReported()
+    {
+        if (OperatingSystem.IsWindows())
+            throw new SkipException("Unix file modes deny the read on Linux/macOS");
+
+        Machine().Save(_path);
+        File.SetUnixFileMode(_path, UnixFileMode.None);
+        Skip.If(CanRead(_path), "Process can read a mode-000 file (running as root)");
+
+        Assert.True(File.Exists(_path));
+        var loaded = ClampSettings.Load(_path, out var status);
+
+        Assert.Equal(ClampSettingsStatus.Invalid, status);
+        AssertFallback(loaded);
+    }
+
+    [Fact]
+    public void FromRailCapturesANestRailForMachineDefaults()
+    {
+        var rail = new ClampRail(38.1, 15.875, new[] { 152.4, 533.4 });
+
+        var captured = ClampSettings.FromRail(rail, Units.Millimeters, enabled: true);
+
+        Assert.True(captured.Enabled);
+        Assert.Equal(Units.Millimeters, captured.Units);
+        Assert.Equal(38.1, captured.Width);
+        Assert.Equal(15.875, captured.Depth);
+        Assert.Equal(new[] { 152.4, 533.4 }, captured.Centers);
+        Assert.Equal(rail, captured.RailFor(Units.Millimeters));
+
+        var none = ClampSettings.FromRail(null, Units.Inches, enabled: false);
+        AssertFallback(none);
+    }
+
+    private static ClampSettingsStatus LoadStatus(string path)
+    {
+        ClampSettings.Load(path, out var status);
+        return status;
+    }
+
+    private static bool CanRead(string path)
+    {
+        try
+        {
+            using var _ = File.OpenRead(path);
+            return true;
+        }
+        catch (UnauthorizedAccessException)
+        {
+            return false;
+        }
+    }
+}