how much weight can the servos take on them
how much can they move

do you thingk they are strong enough to hold back 7 kg
iam making a catapult and going to use it as a trigger.going to use a servo i have that is the same that came in the kit

No, but it might (and I say might) be strong enough to pull out a small pin that is holding the 7 kg.

You could mount the pin such that it is supported on some rollers or bearings so that there is only a very small force required to pull it out.

thanks guys i will consider it
i might use an old fiser price that i have
ill put a pic of it up when iam done
hoe full it will work