diff --git a/incident-ef7/src/incident/impact.py b/incident-ef7/src/incident/impact.py
index 0bc983f..827f0e2 100644
--- a/incident-ef7/src/incident/impact.py
+++ b/incident-ef7/src/incident/impact.py
@@ -18,7 +18,6 @@
     properties=OrderedDict([
         # required properties
         ('availability_impact', IntegerProperty(min=0, max=100, required=True)),
-        ('extension_type', StringProperty(fixed=None)),  # needed to indicate it's a sub object extension
     ])
 )
 class AvailabilityImpactExt:
@@ -31,7 +30,6 @@ class AvailabilityImpactExt:
     properties=OrderedDict([
         # required properties
         ('loss_type', EnumProperty(vocab.CONFIDENTIALITY_LOSS, required=True)),
-        ('extension_type', StringProperty(fixed=None)),  # needed to indicate it's a sub object extension
         # optional properties
         ('information_type', OpenVocabProperty(vocab.INFORMATION_TYPE)),
         ('record_count', IntegerProperty(min=0)),
@@ -55,7 +53,6 @@ def _check_object_constraints(self):
     properties=OrderedDict([
         # required properties
         ('impact_type', OpenVocabProperty(vocab.EXTERNAL_IMPACT, required=True)),
-        ('extension_type', StringProperty(fixed=None)),  # needed to indicate it's a sub object extension
     ])
 )
 class ExternalImpactExt:
@@ -68,7 +65,6 @@ class ExternalImpactExt:
     properties=OrderedDict([
         # required properties
         ('alteration', EnumProperty(vocab.INTEGRITY_ALTERATION, required=True)),
-        ('extension_type', StringProperty(fixed=None)),  # needed to indicate it's a sub object extension
         # optional properties
         ('information_type', OpenVocabProperty(vocab.INFORMATION_TYPE)),
         ('record_count', IntegerProperty(min=0)),
@@ -91,7 +87,6 @@ def _check_object_constraints(self):
     properties=OrderedDict([
         # required properties
         ('variety', OpenVocabProperty(vocab.ECONOMIC_IMPACT, required=True)),
-        ('extension_type', StringProperty(fixed=None)),  # needed to indicate it's a sub object extension
         # optional properties
         ('conversion_rate', FloatProperty()),
         ('conversion_time', TimestampProperty()),
@@ -168,7 +163,6 @@ def _check_object_constraints(self):
     properties=OrderedDict([
         # required properties
         ('impact_type', EnumProperty(vocab.PHYSICAL_IMPACT, required=True)),
-        ('extension_type', StringProperty(fixed=None)),  # needed to indicate it's a sub object extension
         # optional properties
         ('asset_type', OpenVocabProperty(vocab.ASSET_TYPE))
     ])
@@ -188,7 +182,6 @@ def _check_object_constraints(self):
     properties=OrderedDict([
         # required properties
         ('traceability_impact', EnumProperty(vocab.TRACEABILITY_IMPACT, required=True)),
-        ('extension_type', StringProperty(fixed=None)),  # needed to indicate it's a sub object extension
     ])
 )
 class TraceabilityImpactExt:
diff --git a/observed-string-8b1/src/observed_string/observed_string.py b/observed-string-8b1/src/observed_string/observed_string.py
index 38294d3..c989014 100644
--- a/observed-string-8b1/src/observed_string/observed_string.py
+++ b/observed-string-8b1/src/observed_string/observed_string.py
@@ -1,21 +1,17 @@
 import stix2 
 from .observed_string_ov import STRING_PURPOSE
-from stix2.properties import (OpenVocabProperty,
-                              StringProperty)
+from stix2.properties import (OpenVocabProperty, IDProperty, StringProperty, TypeProperty)
 
 
 OBSERVED_STRING_EXTENSION_ID = "extension-definition--8b1aa84c-5532-4c69-a8e7-b6170facfd3d"
 
 
-@stix2.v21.CustomExtension(
-    applies_to = "sco",
-    type = OBSERVED_STRING_EXTENSION_ID,
-    properties =
-    [
-            # required fields
-            ('purpose', OpenVocabProperty(STRING_PURPOSE, required=True)),
-            ('value', StringProperty(required=True))
-    ]
+@stix2.v21.CustomObservable(
+    'observed-string', [
+        # required fields
+        ('purpose', OpenVocabProperty(STRING_PURPOSE, required=True)),
+        ('value', StringProperty(required=True))
+    ], ['purpose', 'value'], OBSERVED_STRING_EXTENSION_ID,
 )
 class ObservedString:
-    extension_type = 'new-sco'
+    pass