6.86 N = (mass) x (9.8 m/s²)
Mass = (6.86 N) / (9.8 m/s²)
Mass = (6.86 kg-m/s²) / (9.8 m/s²)
Mass = (6.86/9.8) kg
Mass = 0.7 kilogram
I would use the 500-gram weight and the 200-gram weight, and hang them both from the end of the thread. Then the total mass on the end of the thread is 700 grams. When I take it to Earth, it will weigh 6.86 N .