The ThreadSpecificationId element is the QIF id of the thread specification for the thread characteristic. This must be the QIF id of a thread specification.
The optional xId attribute is a reference to the id of a QIF object in an external document. A QIF object in an external QIF document can be referenced by using references to two QIF ids: the id of the external document reference of type ExternalQIFDocumentReferenceType found in the local document and the id of the object found in the external document.
Source
<xs:element name="ThreadSpecificationId" type="QIFReferenceType"><xs:annotation><xs:documentation>The ThreadSpecificationId element is the QIF id of the thread specification for the thread characteristic. This must be the QIF id of a thread specification.</xs:documentation></xs:annotation></xs:element>
The id attribute is the QIF id of the characteristic, used for referencing.
Source
<xs:complexType name="ThreadCharacteristicDefinitionType"><xs:annotation><xs:documentation>The ThreadCharacteristicDefinitionType defines information that can be common to more than one thread characteristic.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="CharacteristicDefinitionBaseType"><xs:sequence><xs:element name="ThreadSpecificationId" type="QIFReferenceType"><xs:annotation><xs:documentation>The ThreadSpecificationId element is the QIF id of the thread specification for the thread characteristic. This must be the QIF id of a thread specification.</xs:documentation></xs:annotation></xs:element></xs:sequence></xs:extension></xs:complexContent></xs:complexType>