Summary

Finally see what spring is what (M90-M160). Ment to be pulled by 6,5kg of force.
Cut a piece of M4 or M5 thread about 20cm long and put a big washer inbetween two nuts on the end.
insert the spring, put the thread through and pull on the thread sticking out underneath. Where the washer
stops will be your indication of the typ of spring.