diff --git a/cura/Machines/ContainerGroup.py b/cura/Machines/ContainerGroup.py
deleted file mode 100644
index 0167b3eebe..0000000000
--- a/cura/Machines/ContainerGroup.py
+++ /dev/null
@@ -1,51 +0,0 @@
-# Copyright (c) 2018 Ultimaker B.V.
-# Cura is released under the terms of the LGPLv3 or higher.
-
-from typing import List, Optional
-
-from PyQt5.Qt import QObject, pyqtSlot
-
-from cura.Machines.ContainerNode import ContainerNode
-
-
-#
-# A ContainerGroup represents a group of containers that must be applied to each ContainerStack when it's used.
-# Some concrete examples are Quality and QualityChanges: when we select quality type "normal", this quality type
-# must be applied to all stacks in a machine, although each stack can have different containers. Use an Ultimaker 3
-# as an example, suppose we choose quality type "normal", the actual InstanceConstainers on each stack may look
-# as below:
-#                       GlobalStack         ExtruderStack 1         ExtruderStack 2
-# quality container:    um3_global_normal   um3_aa04_pla_normal     um3_aa04_abs_normal
-#
-# This ContainerGroup is mainly used in quality and quality_changes to group the containers that can be applied to
-# a machine, so when a quality/custom quality is selected, the container can be directly applied to each stack instead
-# of looking them up again.
-#
-class ContainerGroup(QObject):
-
-    def __init__(self, name: str, parent = None):
-        super().__init__(parent)
-        self.name = name
-        self.node_for_global = None  # type: Optional[ContainerNode]
-        self.nodes_for_extruders = dict()
-
-    @pyqtSlot(result = str)
-    def getName(self) -> str:
-        return self.name
-
-    def getAllKeys(self) -> set:
-        result = set()
-        for node in [self.node_for_global] + list(self.nodes_for_extruders.values()):
-            if node is None:
-                continue
-            for key in node.getContainer().getAllKeys():
-                result.add(key)
-        return result
-
-    def getAllNodes(self) -> List[ContainerNode]:
-        result = []
-        if self.node_for_global is not None:
-            result.append(self.node_for_global)
-        for extruder_node in self.nodes_for_extruders.values():
-            result.append(extruder_node)
-        return result
diff --git a/cura/Machines/QualityManager.py b/cura/Machines/QualityManager.py
index be8488fa61..0bb2be1f89 100644
--- a/cura/Machines/QualityManager.py
+++ b/cura/Machines/QualityManager.py
@@ -1,16 +1,14 @@
 # Copyright (c) 2018 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 
-from typing import Optional
+from typing import Optional, List
 
-from PyQt5.Qt import pyqtSignal
-from PyQt5.QtCore import QObject, QTimer
+from PyQt5.QtCore import QObject, QTimer, pyqtSignal, pyqtSlot
 
 from UM.Application import Application
 from UM.Logger import Logger
 from UM.Util import parseBool
 
-from cura.Machines.ContainerGroup import ContainerGroup
 from cura.Machines.ContainerNode import ContainerNode
 
 
@@ -29,14 +27,50 @@ from cura.Machines.ContainerNode import ContainerNode
 #       + <quality_changes_name>
 #
 
-
-class QualityGroup(ContainerGroup):
+#
+# A QualityGroup represents a group of containers that must be applied to each ContainerStack when it's used.
+# Some concrete examples are Quality and QualityChanges: when we select quality type "normal", this quality type
+# must be applied to all stacks in a machine, although each stack can have different containers. Use an Ultimaker 3
+# as an example, suppose we choose quality type "normal", the actual InstanceContainers on each stack may look
+# as below:
+#                       GlobalStack         ExtruderStack 1         ExtruderStack 2
+# quality container:    um3_global_normal   um3_aa04_pla_normal     um3_aa04_abs_normal
+#
+# This QualityGroup is mainly used in quality and quality_changes to group the containers that can be applied to
+# a machine, so when a quality/custom quality is selected, the container can be directly applied to each stack instead
+# of looking them up again.
+#
+class QualityGroup(QObject):
 
     def __init__(self, name: str, quality_type: str, parent = None):
-        super().__init__(name, parent)
+        super().__init__(parent)
+        self.name = name
+        self.node_for_global = None  # type: Optional["QualityGroup"]
+        self.nodes_for_extruders = dict()  # position str -> QualityGroup
         self.quality_type = quality_type
         self.is_available = False
 
+    @pyqtSlot(result = str)
+    def getName(self) -> str:
+        return self.name
+
+    def getAllKeys(self) -> set:
+        result = set()
+        for node in [self.node_for_global] + list(self.nodes_for_extruders.values()):
+            if node is None:
+                continue
+            for key in node.getContainer().getAllKeys():
+                result.add(key)
+        return result
+
+    def getAllNodes(self) -> List["QualityGroup"]:
+        result = []
+        if self.node_for_global is not None:
+            result.append(self.node_for_global)
+        for extruder_node in self.nodes_for_extruders.values():
+            result.append(extruder_node)
+        return result
+
 
 class QualityChangesGroup(QualityGroup):