Armstrong 64-718 3/8" Drive 12 Point Metric Torque Wrench Adapter 18MM 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