diff --git a/bbp_ng/OP_ADDS_rail.py b/bbp_ng/OP_ADDS_rail.py
index a247e86..ce090ec 100644
--- a/bbp_ng/OP_ADDS_rail.py
+++ b/bbp_ng/OP_ADDS_rail.py
@@ -156,7 +156,7 @@ class SharedScrewRailInputProperty():
     rail_screw_steps: bpy.props.IntProperty(
         name = "Steps",
         description = "The segment count per iteration. More segment, more smooth but lower performance.",
-        default = 16,
+        default = 28,
         min = 1,
     ) # type: ignore
 
diff --git a/bbp_ng/UTIL_blender_mesh.py b/bbp_ng/UTIL_blender_mesh.py
index 6513d6f..04ba23c 100644
--- a/bbp_ng/UTIL_blender_mesh.py
+++ b/bbp_ng/UTIL_blender_mesh.py
@@ -107,8 +107,8 @@ class TemporaryMesh():
     
     """
     
-    __mBindingObject: bpy.types.Object | None
-    __mTempMesh: bpy.types.Mesh | None
+    __mBindingObject: bpy.types.Object
+    __mTempMesh: bpy.types.Mesh
     
     def __init__(self, binding_obj: bpy.types.Object):
         self.__mBindingObject = binding_obj
@@ -149,7 +149,7 @@ class MeshReader():
     A helper class TemporaryMesh can help you do this.
     """
     
-    __mAssocMesh: bpy.types.Mesh | None ##< The binding mesh for this reader. None if this reader is invalid.
+    __mAssocMesh: bpy.types.Mesh ##< The binding mesh for this reader. None if this reader is invalid.
     
     def __init__(self, assoc_mesh: bpy.types.Mesh):
         self.__mAssocMesh = assoc_mesh
@@ -318,7 +318,7 @@ class MeshWriter():
     then refer it to all face uv.
     """
     
-    __mAssocMesh: bpy.types.Mesh | None ##< The binding mesh for this writer. None if this writer is invalid.
+    __mAssocMesh: bpy.types.Mesh ##< The binding mesh for this writer. None if this writer is invalid.
     
     __mVertexPos: array.array ##< Array item is float(f). Length must be an integer multiple of 3.
     __mVertexNormal: array.array ##< Array item is float(f). Length must be an integer multiple of 3.