The orthodontists generally do not recommend application of force system above the archwire level owing to additional attachments and patient’s discomfort. Hence, the present research study focusses on application of retraction force system at the archwire level. The objective of this study is to specify an optimum combination of archwire and bracket slot size for en-masse (simultaneous) parallel retraction of six maxillary anterior teeth in labial orthodontics (LaO). In this research study, the concept (theoretical) model has been developed based on simple principles of mechanics to estimate the torque generated by different sizes of archwire in bracket slots. Based on torque value, retraction force developed by each combination of archwire and slot size was determined and compared with required retraction force of 150 gram-force on each side of sagittal plane. For combination of 0.019×0.025 inch stalinless steel SS archwire and 0.022 inch SS bracket slot, magnitude of computed retraction force matched closely with aforementioned required force than other combinations and hence, it is recommended in the present research study. The validation of selected combination of archwire and bracket slot size was done successfully by in vivo (clinical) experimentation on three patients. Thus, it proves that the aforementioned combination of archwire and bracket slot size is more suitable than others for retraction force system applied at archwire level.