The purpose is a part that mounts the inlet and outlet pipes of an external filter, and the product name is neo Holder.

The aquarium fixing parts are fastened with bolts.
It is firmly fixed even if you turn it by hand with gloves on.
It is neatly mounted inside the aquarium without any parts such as bolts.

This is an image shot when it is actually installed.
The nut also holds firmly even when turned with your fingertips without a spanner.
One product can be mounted up to 12 mm thick glass
It is fixed up to ~ 18 mm diameter inlet and outlet pipes.