Long ago in a place far away... (Michigan), I decided I wanted to have a different wing hold-down than the 'standard' 1/2in square extrusion with a 3/8in tapped hole in the end, leaving only about 1/16in 'meat' around the tapped hole. I decided to machine a 'dogbone' shaped set of hold-downs with a tapered 'beam' between the top and bottom spar strips. The 'ears' of the hold-down are approximately 1/8in thick & the end with the tapped hole is approximately 5/8in x 5/8in. The 'beam' portion of the hold-down is 'grooved' to accept two AN3 bolts with built-in stand-offs equal to the height of the spar strips that the dog-bone rests on... This has the hold-down attached to the front of the spar (as some others have done), rather than within the 'C-channel' so there is no need for a hole in the spar flange.
