Most gliders require different types of weak links for aerotow or winch launch. For the Libelle it is the same type for both types of launches; a white weak link of 5 kilo Newton.
The weak link is crucial for protecting the plane’s structure. When there is too much force from the cable on the hull of the plane, i.e. when there is a gust of wind, or when the winch speed is too high. The weak link breaks when too much force is present, hence protecting the glider, but more importantly the pilot.
The type of weak link that your glider requires, is always specified in the flight manual of the specific plane. The number of these white ones (5) coincidentally occurs to match the maximum of kN allowed. However, that is only the case for these white number fives. The limit of kN force allowed on weak links ranges roughly from 1-10 kN. The lower numbers are generally allowing for more force (i.e. number 1, black, is strong enough for 10kN) whereas the higher numbers are more sensitive (i.e. number 11, orange, is snapping at 0.8kN). In the Netherlands we use the color coding it does not matter just make sure you use the one specified in the flight manual. And keep in mind the launch method you use.

For some people the inconvenience of switching all the time, or having to abort a start when the weak link snaps at a low altitude outweighs the intended use of these weak links. Using a weak link that allows for plenty of force or tension is then a sought after solution, not only used by individuals but also glider clubs.
When using the wrong weak link, damage to the construction of your tow hook and fuselage can occur. This can be hard to spot and expensive to fix. I didn’t find references of tow hooks coming loose but I can imagine it ruins your happy day when it does.

Make sure that your plane or you do not become the weakest link, but purchase the suitable weak link for your glider.] So if you care about your plane’s health and your own, only use the specified weak link. They cost 5-6 Euro or something like that. This is not a sponsored, yet a purely informative post .