.. Hex key

The gold pen could be used as a hex key. It has six sides. ( You can find the gold pen in Sgt. Crabulous junk piles )

You would need to bend the pen so that it becomes a hex key.

Have you inserted the pen into snug holes, lately?

There is a hole outside the mansion. Put the pen into the hole.

You can try to bend the pen with "Use" action on the pen in the hole.

Not with bare hands. Does Mr. Fumble help you?

Mr. Fumble said you should just whack the pen with something. Try to find something heavy that is good for hitting.

Grab the long branch near the tree. Use the long branch on the pen in the hole to make a hex key.