Armstrong 64-755 3/8" Drive 12 Point SAE Torque Wrench Adapter 9/16" Changes A 3/8" Square Drive Torque Wrench (Or Ratchet) Into A 12-Pt. Box End Wrench Configuration The Box End Wall Thickness is Specially Designed to Provide Strength While Still Allowing Ample Room for Access to Reach Restricted Fasteners. Measure Exactly 2 Inches From Center of Adapter Opening (Fastener) to the Center of Square Drive for Easy Torque Calculations {Desired Torque to Fastener Length of Torque Wrench} / {Length of Torque Wrench Adapter Center to Center Distance (2")} This Calculation Assumes That the Attachment is Aligned with Torque Wrench Handle When Torqueing Fastener