Kavan in Germany makes these extraordinary strong for fine adjustment of flying and bracing cable on scale model airplanes.
We went ahead and had our own tensile strength tests done and the results surpassed what we were hoping for. The M2 nickel-plated brass turnbuckles held up to 100lbs each while the M3 brass turnbuckles held up to 350lbs each. Please note, these were non-scientific test, we simply loaded a bucket with bricks until the turnbuckle gave way.
If you do the math you will see how these two turnbuckles will serve all your miniature aircraft needs.
Dr. Vogelsang is using the M3s on his 1:2.2 scale Fly Baby as well as his 1:2 scale Bücker Jungmeister. The M2s find use in tail feather applications, for example.
M2 nickel-plated brass turnbuckle
Length: 0.8 - 1.1 inches
Eyebolt: 0.067 inches
Max tested load, no guarantee: 100 lbs
M3 brass turnbuckle
Length: 20. - 2.9 inches
Eyebolt: 0.1 inches
Max tested load, no guarantee : 350 lbs