So just building been as well; the flap arm is .75" . For The ailerons, I'm using a durable plastic arm for the clevis pins, .80" as the arm just exists the slit opening.
The Elevator will be .75" on a carbon arm from MKS, $7 an arm . Rudder will use a .80 arm for the clevis but if it doesn't fit will go to 1" with a ball link to clear the opening slit.
Hope this helps Vegasking.