This is a template attribute. Template attributes can be used in filtering, or to retrieve data from the model to use in drawings and reports. For example, when you create a report, Tekla Structures replaces the attributes added in the report template with the corresponding object property values.

Shows the assembly position number. For parts ASSEMBLY_POS shows the assembly position number of the assembly that contains the part. For reinforcement objects ASSEMBLY_POS shows the assembly position number of the rebar assembly that contains the reinforcement object. For bolts the field is blank.