This pic shows the way the older style sending units supported the intank pump, and held them in place.

That holder supported the pump around a band that was part of the pump housing...

...to support the pump's weight
...to locate the pump at the right height above the bottom of the tank

It also shows the common failure of the older style sock filters: deterioration and separation of the filter material.

...not a good thing to let any kind of debris get into the pump.