Wrench size needed for SR-A10 extension shaft coupler? Shawn February 16, 2021 17:16 Updated You will need a 12mm wrench and a 14mm wrench. The picture below shows the proper placement of the wrenches. Related articles Common factors that cause high SWR readings Looking to get a new whip for my Stryker Antenna. Comments 0 comments Article is closed for comments.