diff --git a/freecad/gears/features.py b/freecad/gears/features.py
index 9e22226..186b02e 100644
--- a/freecad/gears/features.py
+++ b/freecad/gears/features.py
@@ -206,7 +206,7 @@ class InvoluteGearRack(object):
         obj.addProperty(
             "App::PropertyFloat", "head", "gear_parameter", "head * module = additional length of head")
         obj.addProperty(
-            "App::PropertyFloat", "clearence", "gear_parameter", "clearence * module = additional length of foot")
+            "App::PropertyFloat", "clearance", "gear_parameter", "clearance * module = additional length of foot")
         obj.addProperty(
             "App::PropertyBool", "properties_from_tool", "gear_parameter", "if beta is given and properties_from_tool is enabled, \
             gear parameters are internally recomputed for the rotated gear")
@@ -225,7 +225,7 @@ class InvoluteGearRack(object):
         obj.height = '5. mm'
         obj.thickness = '5 mm'
         obj.beta = '0. deg'
-        obj.clearence = 0.25
+        obj.clearance = 0.25
         obj.head = 0.
         obj.properties_from_tool = True
         obj.add_endings = True
@@ -241,8 +241,8 @@ class InvoluteGearRack(object):
         fp.rack.beta = fp.beta.Value * np.pi / 180.
         fp.rack.head = fp.head
         # checksbackwardcompatibility:
-        if "clearence" in fp.PropertiesList:
-            fp.rack.clearence = fp.clearence
+        if "clearance" in fp.PropertiesList:
+            fp.rack.clearance = fp.clearance
         if "properties_from_tool" in fp.PropertiesList:
             fp.rack.properties_from_tool = fp.properties_from_tool
         if "add_endings" in fp.PropertiesList:
@@ -615,14 +615,14 @@ class WormGear(object):
         obj.addProperty(
             "App::PropertyFloat", "head", "gear_parameter", "head * module = additional length of head")
         obj.addProperty(
-            "App::PropertyFloat", "clearence", "gear_parameter", "clearence * module = additional length of foot")
+            "App::PropertyFloat", "clearance", "gear_parameter", "clearance * module = additional length of foot")
 
         obj.teeth = 3
         obj.module = '1. mm'
         obj.pressure_angle = '20. deg'
         obj.height = '5. mm'
         obj.diameter = '5. mm'
-        obj.clearence = 0.25
+        obj.clearance = 0.25
         obj.head = 0
 
         self.obj = obj
@@ -634,18 +634,18 @@ class WormGear(object):
         t = fp.teeth
         h = fp.height
 
-        clearence = fp.clearence
+        clearance = fp.clearance
         head = fp.head
         alpha = fp.pressure_angle.Value
         beta = np.arctan(m * t / d)
         fp.beta = np.rad2deg(beta)
         beta = np.pi / 2 - beta
 
-        r_1 = (d - (2 + 2 * clearence) * m) / 2
+        r_1 = (d - (2 + 2 * clearance) * m) / 2
         r_2 = (d + (2 + 2 * head) * m) / 2
-        z_a = (2 + head + clearence) * m * np.tan(np.deg2rad(alpha))
+        z_a = (2 + head + clearance) * m * np.tan(np.deg2rad(alpha))
         z_b = (m * np.pi - 4 * m * np.tan(np.deg2rad(alpha))) / 2
-        z_0 = clearence * m * np.tan(np.deg2rad(alpha))
+        z_0 = clearance * m * np.tan(np.deg2rad(alpha))
         z_1 = z_b - z_0
         z_2 = z_1 + z_a
         z_3 = z_2 + z_b - 2 * head * m * np.tan(np.deg2rad(alpha))
diff --git a/pygears/involute_tooth.py b/pygears/involute_tooth.py
index 051e480..da95e5b 100644
--- a/pygears/involute_tooth.py
+++ b/pygears/involute_tooth.py
@@ -160,7 +160,7 @@ class InvoluteTooth():
 
 
 class InvoluteRack(object):
-    def __init__(self, m=5, z=15, pressure_angle=20 * pi / 180., thickness=5, beta=0, head=0, clearence=0.25, 
+    def __init__(self, m=5, z=15, pressure_angle=20 * pi / 180., thickness=5, beta=0, head=0, clearance=0.25, 
                  properties_from_tool=False, add_endings=False, simplified=False):
         self.pressure_angle = pressure_angle
         self.thickness = thickness
@@ -168,7 +168,7 @@ class InvoluteRack(object):
         self.z = z
         self.beta = beta
         self.head = head
-        self.clearence = clearence
+        self.clearance = clearance
         self.properties_from_tool = properties_from_tool
         self.add_endings = add_endings
         self.simplified = simplified
@@ -185,13 +185,13 @@ class InvoluteRack(object):
         import copy
         m, m_n, pitch, pressure_angle_t = self.compute_properties()
 
-        a = (2 + self.head + self.clearence) * m_n * tan(pressure_angle_t)
+        a = (2 + self.head + self.clearance) * m_n * tan(pressure_angle_t)
         b = pitch / 4 - (1 + self.head) * m_n * tan(pressure_angle_t)
         tooth = [
-            [-m_n * (1 + self.clearence), -a - b],
+            [-m_n * (1 + self.clearance), -a - b],
             [m_n * (1 + self.head), -b],
             [m_n * (1 + self.head), b],
-            [-m_n * (1 + self.clearence), a + b]
+            [-m_n * (1 + self.clearance), a + b]
         ]
         teeth = [tooth]
         trans = translation([0., pitch, 0.])