diff --git a/designs/duct_takeoff_starting_collar/family.json b/designs/duct_takeoff_starting_collar/family.json
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+{
+  "family": "duct_takeoff_starting_collar",
+  "standard": "GreenSeam / ECCO / M&M round-duct start collar (SMACNA)",
+  "base_plane": "XY",
+  "description": "Round-duct takeoff/starting collar: a rolled sheet-metal barrel with a stiffening top bead, a ring of rectangular base tabs (the real trapezoidal tabs simplified) that bend flat onto the duct, and an optional integral butterfly damper on a diametral shaft. One solid.",
+  "source": "GreenSeam tabbed/spin-in start-collar spec sheets + ECCO / M&M submittals (diameter, body, bead, tabs, damper); gauge per ASTM A653 / SMACNA; tab count/width proportion",
+  "contributor": "BenchCAD-org"
+}
diff --git a/designs/duct_takeoff_starting_collar/part.py b/designs/duct_takeoff_starting_collar/part.py
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+++ b/designs/duct_takeoff_starting_collar/part.py
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+"""duct_takeoff_starting_collar — the parametric part.
+
+A round-duct takeoff / starting collar: a short galvanized sheet-metal round
+collar (barrel) that starts a round branch off a plenum or main duct. A rolled
+bead stiffens the top (slip-fit) end, the base carries a ring of rectangular tabs
+(the real trapezoidal tabs are simplified to rectangles) that bend flat, and an optional butterfly damper sits on a
+diametral shaft inside the barrel. The barrel axis is Z; the tabs lie in the
+mounting plane at z=0.
+
+Interface + examples: docs/DESIGN_SPEC.md
+"""
+
+import cadquery as cq
+
+
+def _tab_angles(count):
+    """Angular position (deg) of each base tab."""
+    return [360.0 * i / count for i in range(count)]
+
+
+def build(collar_d, collar_h, wall, bead_proj, tab_h, tab_w, tab_count, damper):
+    r_out = collar_d / 2.0
+    r_in = r_out - wall
+
+    # straight collar barrel (annular tube) along Z, z in [0, collar_h]
+    result = cq.Workplane("XY").circle(r_out).circle(r_in).extrude(collar_h)
+
+    # rolled bead: an outward stiffening rib around the slip-fit (top) end
+    bead_h = wall * 4.0
+    bead = (
+        cq.Workplane("XY")
+        .circle(r_out + bead_proj)
+        .circle(r_in)
+        .extrude(bead_h)
+        .translate((0.0, 0.0, collar_h - bead_h))
+    )
+    result = result.union(bead)
+
+    # base tabs: flat rectangular tabs (real ones trapezoidal) bent out into the mounting plane
+    for ang in _tab_angles(tab_count):
+        tab = (
+            cq.Workplane("XY")
+            .box(tab_h, tab_w, wall)
+            .translate((r_out + tab_h / 2.0 - wall, 0.0, wall / 2.0))
+            .rotate((0.0, 0.0, 0.0), (0.0, 0.0, 1.0), ang)
+        )
+        result = result.union(tab)
+
+    # optional butterfly damper: a blade disc on a diametral shaft, mid-barrel.
+    # The blade runs a running clearance inside the bore (not bore-sized) so its
+    # union is not a fragile coincident-face touch; the shaft ties it to the barrel.
+    if damper:
+        z_mid = collar_h / 2.0
+        blade_gap = max(1.0, wall)
+        blade = cq.Workplane("XY").circle(r_in - blade_gap).extrude(wall, both=True).translate((0.0, 0.0, z_mid))
+        shaft_l = collar_d + 20.0
+        shaft = cq.Workplane("YZ").circle(3.0).extrude(shaft_l).translate((-shaft_l / 2.0, 0.0, z_mid))
+        result = result.union(blade).union(shaft)
+
+    return result
diff --git a/designs/duct_takeoff_starting_collar/preview.png b/designs/duct_takeoff_starting_collar/preview.png
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diff --git a/designs/duct_takeoff_starting_collar/preview_extremes.png b/designs/duct_takeoff_starting_collar/preview_extremes.png
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diff --git a/designs/duct_takeoff_starting_collar/preview_views.png b/designs/duct_takeoff_starting_collar/preview_views.png
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diff --git a/designs/duct_takeoff_starting_collar/spec.py b/designs/duct_takeoff_starting_collar/spec.py
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+++ b/designs/duct_takeoff_starting_collar/spec.py
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+"""duct_takeoff_starting_collar — the benchmark generator spec.
+
+A round-duct takeoff / starting collar (tabbed, optional butterfly damper).
+PARAM_SPEC declares each build() parameter; check() holds the engineering rules a
+reviewer audits. Nothing is coupled, so there is no refine().
+Spec: docs/DESIGN_SPEC.md
+
+Sources:
+- GreenSeam tabbed / spin-in start collar spec sheets + ECCO and M&M submittals:
+  collar (branch) Ø 4-20 in (100-500 mm), cylindrical body ~6 in, crimp/bead
+  1-5/8 in, base tabs ~1 in, ~16 trapezoidal tabs, damper axis 2 in below the
+  bead. Galvanized steel ASTM A653, 26 ga std / 24 ga option.
+- Only diameter varies per catalog row (lengths constant); tab count/width not
+  dimensioned -> "proportion".
+"""
+
+
+# ── 1. PARAM_SPEC ────────────────────────────────────────────────────────────
+PARAM_SPEC = {
+    "collar_d": dict(
+        desc="collar (branch-duct) nominal diameter",
+        unit="mm",
+        range={"easy": (150.0, 300.0), "medium": (100.0, 400.0), "hard": (100.0, 500.0)},
+        source="GreenSeam/ECCO/M&M start-collar sizes 4-20 in (100-500 mm)",
+        askable=True,
+    ),
+    "collar_h": dict(
+        desc="cylindrical barrel height",
+        unit="mm",
+        range={"easy": (80.0, 120.0), "medium": (60.0, 150.0), "hard": (55.0, 160.0)},
+        source="GreenSeam ~6 in body -> proportion",
+        askable=True,
+    ),
+    "wall": dict(
+        desc="sheet-metal wall thickness",
+        unit="mm",
+        range={"easy": (0.5, 0.7), "medium": (0.5, 0.85), "hard": (0.4, 0.9)},
+        source="26 ga (0.55 mm) / 24 ga (0.7 mm) galvanized, ASTM A653",
+        askable=True,
+    ),
+    "bead_proj": dict(
+        desc="outward projection of the rolled top bead",
+        unit="mm",
+        range={"easy": (2.0, 4.0), "medium": (2.0, 5.0), "hard": (1.5, 6.0)},
+        source="proportion (rolled stiffening bead)",
+        askable=True,
+    ),
+    "tab_h": dict(
+        desc="mounting-tab length (radial reach)",
+        unit="mm",
+        range={"easy": (20.0, 28.0), "medium": (15.0, 32.0), "hard": (12.0, 35.0)},
+        source="GreenSeam tab ~1 in (25 mm)",
+        askable=True,
+    ),
+    "tab_w": dict(
+        desc="mounting-tab width",
+        unit="mm",
+        range={"easy": (12.0, 18.0), "medium": (10.0, 22.0), "hard": (8.0, 26.0)},
+        source="proportion (tab width not dimensioned; ~16 tabs on the photo)",
+        askable=True,
+    ),
+    "tab_count": dict(
+        desc="number of base mounting tabs",
+        unit="",
+        range={"easy": (14, 18), "medium": (12, 20), "hard": (10, 24)},
+        source="GreenSeam photo ~16 trapezoidal tabs -> proportion",
+        integer=True,
+        askable=True,
+    ),
+    "damper": dict(
+        desc="integral butterfly damper (blade + shaft) fitted (1) vs none (0)",
+        unit="",
+        range={"easy": (0, 0), "medium": (0, 1), "hard": (0, 1)},
+        source="GreenSeam/ECCO with-damper vs plain start-collar variants",
+        choices={"easy": [0], "medium": [0, 1], "hard": [0, 1]},
+        feature=True,
+    ),
+}
+
+
+# ── 2. check ─────────────────────────────────────────────────────────────────
+def check(p: dict) -> list[str]:
+    """Engineering constraints (empty = valid). Each cites its rule."""
+    import math
+
+    bad = []
+
+    # the tabs must fit around the base circumference with gaps between them
+    if p["tab_count"] * p["tab_w"] > 0.9 * math.pi * p["collar_d"]:
+        bad.append("tab_count*tab_w > 0.9*pi*D: tabs overlap around the base")
+
+    # rolled sheet, not thick pipe
+    if p["wall"] > p["collar_d"] / 60.0:
+        bad.append("wall > D/60: collar is rolled sheet metal, not thick pipe")
+
+    # the bead must be smaller than the mounting tabs
+    if p["bead_proj"] > p["tab_h"]:
+        bad.append("bead_proj > tab_h: bead should be a small rib, not larger than a tab")
+
+    # a barrel, not a flat ring: body height must exceed the wall bead zone
+    if p["collar_h"] < 6.0 * p["wall"] + 20.0:
+        bad.append("collar_h too short: barrel must clear the bead zone with a real body")
+
+    return bad