diff --git a/nhf/parts/fasteners.py b/nhf/parts/fasteners.py
index c6a0afe..78d7cfc 100644
--- a/nhf/parts/fasteners.py
+++ b/nhf/parts/fasteners.py
@@ -4,6 +4,42 @@ import cadquery as Cq
 from nhf import Item, Role
 import nhf.utils
 
+@dataclass(frozen=True)
+class FlatHeadBolt(Item):
+    diam_head: float
+    height_head: float
+    diam_thread: float
+    height_thread: float
+
+    @property
+    def name(self) -> str:
+        return f"Bolt M{int(self.diam_thread)} h{int(self.height_thread)}mm"
+
+
+    def generate(self) -> Cq.Assembly:
+        print(self.name)
+        head = Cq.Solid.makeCylinder(
+            radius=self.diam_head / 2,
+            height=self.height_head,
+        )
+        rod = (
+            Cq.Workplane('XY')
+            .cylinder(
+                radius=self.diam_thread/ 2,
+                height=self.height_thread,
+                centered=(True, True, False))
+        )
+        rod.faces("<Z").tag("tip")
+        rod.faces(">Z").tag("root")
+
+        return (
+            Cq.Assembly()
+            .addS(rod, name="thread", role=Role.CONNECTION)
+            .addS(head, name="head", role=Role.CONNECTION,
+                  loc=Cq.Location((0, 0, self.height_thread)))
+        )
+
+
 @dataclass(frozen=True)
 class ThreaddedKnob(Item):
     """
@@ -12,8 +48,8 @@ class ThreaddedKnob(Item):
     > Othmro Black 12mm(M12) x 50mm Thread Replacement Star Hand Knob Tightening
     > Screws
     """
-    diam_rod: float
-    height_rod: float
+    diam_thread: float
+    height_thread: float
     diam_knob: float
 
     diam_neck: float
@@ -22,7 +58,7 @@ class ThreaddedKnob(Item):
 
     @property
     def name(self) -> str:
-        return f"Knob-M{int(self.diam_rod)}-{int(self.height_rod)}mm"
+        return f"Knob M{int(self.diam_thread)} h{int(self.height_thread)}mm"
 
     def generate(self) -> Cq.Assembly:
         print(self.name)
@@ -34,41 +70,40 @@ class ThreaddedKnob(Item):
             radius=self.diam_neck / 2,
             height=self.height_neck,
         )
-        rod = (
+        thread = (
             Cq.Workplane('XY')
             .cylinder(
-                radius=self.diam_rod / 2,
-                height=self.height_rod,
+                radius=self.diam_thread / 2,
+                height=self.height_thread,
                 centered=(True, True, False))
         )
-        rod.faces("<Z").tag("tip")
-        rod.faces(">Z").tag("root")
+        thread.faces("<Z").tag("tip")
+        thread.faces(">Z").tag("root")
 
         return (
             Cq.Assembly()
-            .addS(rod, name="rod", role=Role.CONNECTION)
+            .addS(thread, name="thread", role=Role.CONNECTION)
             .addS(neck, name="neck", role=Role.HANDLE,
-                  loc=Cq.Location((0, 0, self.height_rod)))
+                  loc=Cq.Location((0, 0, self.height_thread)))
             .addS(knob, name="knob", role=Role.HANDLE,
-                  loc=Cq.Location((0, 0, self.height_rod + self.height_neck)))
+                  loc=Cq.Location((0, 0, self.height_thread + self.height_neck)))
         )
 
 
 @dataclass(frozen=True)
 class HexNut(Item):
-    diam: float
+    diam_thread: float
     pitch: float
 
-    # FIXME: Measure these
-    m: float
-    s: float
+    thickness: float
+    width: float
 
     def __post_init__(self):
-        assert self.s > self.diam
+        assert self.width > self.diam_thread
 
     @property
     def name(self):
-        return f"HexNut-M{int(self.diam)}-{self.pitch}"
+        return f"HexNut M{int(self.diam_thread)}-{self.pitch}"
 
     @property
     def role(self):
@@ -76,14 +111,14 @@ class HexNut(Item):
 
     def generate(self) -> Cq.Workplane:
         print(self.name)
-        r = self.s / math.sqrt(3)
+        r = self.width / math.sqrt(3)
         result = (
             Cq.Workplane("XY")
             .sketch()
             .regularPolygon(r=r, n=6)
-            .circle(r=self.diam/2, mode='s')
+            .circle(r=self.diam_thread/2, mode='s')
             .finalize()
-            .extrude(self.m)
+            .extrude(self.thickness)
         )
         result.faces("<Z").tag("bot")
         result.faces(">Z").tag("top")
diff --git a/nhf/parts/item.py b/nhf/parts/item.py
index 16fbef7..1e321fc 100644
--- a/nhf/parts/item.py
+++ b/nhf/parts/item.py
@@ -31,17 +31,17 @@ class Item:
     def role(self) -> Optional[Role]:
         return None
 
-    def generate(self) -> Union[Cq.Assembly, Cq.Workplane]:
+    def generate(self, **kwargs) -> Union[Cq.Assembly, Cq.Workplane]:
         """
         Creates an assembly for this item. Subclass should implement this
         """
         return Cq.Assembly()
 
-    def assembly(self) -> Cq.Assembly:
+    def assembly(self, **kwargs) -> Cq.Assembly:
         """
         Interface for creating assembly with the necessary metadata
         """
-        a = self.generate()
+        a = self.generate(**kwargs)
         if isinstance(a, Cq.Workplane):
             a = Cq.Assembly(a)
             if role := self.role:
diff --git a/nhf/parts/joints.py b/nhf/parts/joints.py
index 8602147..31bb686 100644
--- a/nhf/parts/joints.py
+++ b/nhf/parts/joints.py
@@ -180,6 +180,7 @@ class TorsionJoint:
     3. An outer and an inner annuli which forms a track the rider can move on
     """
     spring: TorsionSpring = field(default_factory=lambda: TorsionSpring(
+        mass=float('nan'),
         radius=10.0,
         thickness=2.0,
         height=15.0,
@@ -306,6 +307,7 @@ class TorsionJoint:
             .hole(self.radius_axle * 2)
             .cut(slot.moved(Cq.Location((0, 0, self.track_disk_height))))
         )
+        result.faces("<Z").tag("bot")
         # Insert directrix
         result.polyline(self._directrix(self.track_disk_height),
                         forConstruction=True).tag("dir")
diff --git a/nhf/parts/springs.py b/nhf/parts/springs.py
index 80c1915..0418122 100644
--- a/nhf/parts/springs.py
+++ b/nhf/parts/springs.py
@@ -2,9 +2,10 @@ import math
 from typing import Optional
 from dataclasses import dataclass
 import cadquery as Cq
+from nhf import Item, Role
 
-@dataclass
-class TorsionSpring:
+@dataclass(frozen=True)
+class TorsionSpring(Item):
     """
     A torsion spring with abridged geometry (since sweep is slow)
     """
@@ -21,6 +22,10 @@ class TorsionSpring:
 
     torsion_rate: Optional[float] = None
 
+    @property
+    def name(self) -> str:
+        return f"TorsionSpring-{int(self.radius)}-{int(self.height)}"
+
     @property
     def radius_inner(self) -> float:
         return self.radius - self.thickness
@@ -28,7 +33,7 @@ class TorsionSpring:
     def torque_at(self, theta: float) -> float:
         return self.torsion_rate * theta
 
-    def generate(self, deflection: float = 0):
+    def generate(self, deflection: float = 0) -> Cq.Workplane:
         omega = self.angle_neutral + deflection
         omega = -omega if self.right_handed else omega
         base = (
@@ -39,7 +44,6 @@ class TorsionSpring:
         base.faces(">Z").tag("top")
         base.faces("<Z").tag("bot")
 
-        box_shift = -self.radius if self.right_handed else self.radius-self.thickness
         tail = Cq.Solid.makeCylinder(
             height=self.tail_length,
             radius=self.thickness / 2)
diff --git a/nhf/parts/test.py b/nhf/parts/test.py
index 6e01420..27ae9a5 100644
--- a/nhf/parts/test.py
+++ b/nhf/parts/test.py
@@ -2,6 +2,25 @@ import unittest
 import cadquery as Cq
 from nhf.checks import binary_intersection, pairwise_intersection
 from nhf.parts import joints, handle, metric_threads, springs
+import nhf.parts.fasteners as fasteners
+
+class TestFasteners(unittest.TestCase):
+
+    def test_hex_nut(self):
+        width = 18.9
+        height = 9.8
+        item = fasteners.HexNut(
+            mass=float('nan'),
+            diam_thread=12.0,
+            pitch=1.75,
+            thickness=9.8,
+            width=width,
+        )
+        obj = item.generate()
+        self.assertEqual(len(obj.vals()), 1)
+        bbox = obj.val().BoundingBox()
+        self.assertAlmostEqual(bbox.xlen, width)
+        self.assertAlmostEqual(bbox.zlen, height)
 
 class TestJoints(unittest.TestCase):
 
diff --git a/nhf/touhou/houjuu_nue/joints.py b/nhf/touhou/houjuu_nue/joints.py
index cb53ae1..04291aa 100644
--- a/nhf/touhou/houjuu_nue/joints.py
+++ b/nhf/touhou/houjuu_nue/joints.py
@@ -5,6 +5,7 @@ import cadquery as Cq
 from nhf import Material, Role
 from nhf.build import Model, target, assembly
 from nhf.parts.springs import TorsionSpring
+from nhf.parts.fasteners import FlatHeadBolt
 from nhf.parts.joints import TorsionJoint
 from nhf.parts.box import Hole, MountingBox, box_with_centre_holes
 import nhf.utils
@@ -14,6 +15,15 @@ TOL = 1e-6
 @dataclass
 class ShoulderJoint(Model):
 
+    bolt: FlatHeadBolt = FlatHeadBolt(
+        # FIXME: measure
+        diam_head=10.0,
+        height_head=3.0,
+        diam_thread=6.0,
+        height_thread=20.0,
+        mass=float('nan'),
+    )
+
     height: float = 60.0
     torsion_joint: TorsionJoint = field(default_factory=lambda: TorsionJoint(
         radius_track=18,
@@ -23,9 +33,9 @@ class ShoulderJoint(Model):
         groove_radius_inner=13,
         track_disk_height=5.0,
         rider_disk_height=5.0,
-        # M8 Axle
         radius_axle=3.0,
         spring=TorsionSpring(
+            mass=float('nan'),
             # inner diameter = 9
             radius=9/2 + 1.2,
             thickness=1.3,
@@ -69,6 +79,16 @@ class ShoulderJoint(Model):
     def __post_init__(self):
         assert self.parent_lip_length * 2 < self.height
 
+    @property
+    def radius(self):
+        return self.torsion_joint.radius
+
+    def parent_arm_loc(self) -> Cq.Location:
+        """
+        2d location of the arm surface on the parent side, relative to axle
+        """
+        return Cq.Location.rot2d(self.angle_neutral) * Cq.Location.from2d(self.parent_lip_ext, 0, 0)
+
     def parent(self, top: bool = False) -> Cq.Assembly:
         joint = self.torsion_joint
         # Thickness of the lip connecting this joint to the wing root
@@ -219,14 +239,18 @@ class ShoulderJoint(Model):
             .constrain("child/core", "Fixed")
             .addS(self.torsion_joint.spring.generate(deflection=-deflection), name="spring_top",
                   role=Role.DAMPING, material=mat_spring)
+            .addS(self.bolt.assembly(), name="bolt_top")
             .addS(self.parent_top(),
                   name="parent_top",
                   role=Role.PARENT, material=mat)
             .addS(self.torsion_joint.spring.generate(deflection=deflection), name="spring_bot",
                   role=Role.DAMPING, material=mat_spring)
+            .addS(self.bolt.assembly(), name="bolt_bot")
             .addS(self.parent_bot(),
                   name="parent_bot",
                   role=Role.PARENT, material=mat)
+            .constrain("bolt_top/thread?root", "parent_top/track?bot", "Plane", param=0)
+            .constrain("bolt_bot/thread?root", "parent_bot/track?bot", "Plane", param=0)
         )
         TorsionJoint.add_constraints(
             result,
@@ -318,6 +342,7 @@ class DiskJoint(Model):
     the housing. This provides torsion resistance.
     """
     spring: TorsionSpring = field(default_factory=lambda: TorsionSpring(
+        mass=float('nan'),
         radius=9 / 2,
         thickness=1.3,
         height=6.5,
@@ -617,7 +642,7 @@ class ElbowJoint(Model):
     parent_arm_angle: float = 180.0
 
     # Size of the mounting holes
-    hole_diam: float = 6.0
+    hole_diam: float = 4.0
 
     material: Material = Material.RESIN_TRANSPERENT
 
@@ -628,6 +653,10 @@ class ElbowJoint(Model):
         assert self.parent_arm_radius > self.disk_joint.radius_housing
         self.disk_joint.tongue_length = self.child_arm_radius - self.disk_joint.radius_disk - self.lip_thickness / 2
 
+    @property
+    def total_thickness(self):
+        return self.disk_joint.total_thickness
+
     def parent_arm_loc(self) -> Cq.Location:
         """
         2d Location of the centre of the arm surface on the parent side, assuming
diff --git a/nhf/touhou/houjuu_nue/wing.py b/nhf/touhou/houjuu_nue/wing.py
index b9e2014..77f51f8 100644
--- a/nhf/touhou/houjuu_nue/wing.py
+++ b/nhf/touhou/houjuu_nue/wing.py
@@ -41,8 +41,8 @@ class WingProfile(Model):
     ))
     shoulder_angle_bias: float = 0.0
     shoulder_width: float = 36.0
-    shoulder_tip_x: float = -200.0
-    shoulder_tip_y: float = 160.0
+    shoulder_tip_x: float = -260.0
+    shoulder_tip_y: float = 165.0
     shoulder_mid_x: float = -105.0
     shoulder_mid_y: float = 75.0
 
@@ -102,7 +102,11 @@ class WingProfile(Model):
         self.elbow_axle_loc = self.elbow_bot_loc * Cq.Location.from2d(0, self.elbow_height / 2)
         self.wrist_axle_loc = self.wrist_bot_loc * Cq.Location.from2d(0, self.wrist_height / 2)
 
+        assert self.elbow_joint.total_thickness < min(self.s1_thickness, self.s2_thickness)
+        assert self.wrist_joint.total_thickness < min(self.s2_thickness, self.s3_thickness)
+
         self.shoulder_joint.angle_neutral = -self.shoulder_angle_neutral - self.shoulder_angle_bias
+        self.shoulder_axle_loc = Cq.Location.from2d(self.shoulder_tip_x, self.shoulder_tip_y - self.shoulder_width / 2, -self.shoulder_angle_bias)
 
     @submodel(name="shoulder-joint")
     def submodel_shoulder_joint(self) -> Model:
@@ -225,6 +229,9 @@ class WingProfile(Model):
                 (-self.base_width, 0),
             )
             .assemble()
+            .push([self.shoulder_axle_loc.to2d_pos()])
+            .circle(self.shoulder_joint.radius, mode='a')
+            .circle(self.shoulder_joint.bolt.diam_head / 2, mode='s')
         )
         return sketch
 
@@ -292,17 +299,12 @@ class WingProfile(Model):
     def surface_s0(self, top: bool = False) -> Cq.Workplane:
         base_dx = -(self.base_width - self.base_plate_width) / 2
         base_dy = self.base_joint.joint_height
-        sw = self.shoulder_width
-
-        axle_dist = self.shoulder_joint.parent_lip_ext
-        theta = math.radians(self.shoulder_angle_neutral)
-        c, s = math.cos(theta), math.sin(theta)
+        loc_tip = Cq.Location(0, -self.shoulder_joint.parent_lip_width / 2)
         tags = [
-            # transforms [axle_dist, -sw/2] about the centre (tip_x, tip_y - sw/2)
-            ("shoulder", Cq.Location.from2d(
-                self.shoulder_tip_x          + axle_dist * c + (-sw/2) * s,
-                self.shoulder_tip_y - sw / 2 - axle_dist * s + (-sw/2) * c,
-                -self.shoulder_angle_neutral)),
+            ("shoulder",
+             self.shoulder_axle_loc *
+             self.shoulder_joint.parent_arm_loc() *
+             loc_tip),
             ("base", Cq.Location.from2d(base_dx,  base_dy, 90)),
         ]
         result = extrude_with_markers(