De or het flensverbinding?

The correct Dutch article is:

de flensverbinding

Rule Words ending in -ing: almost always de. See the rule

How to use flensverbinding

the flensverbindingde flensverbinding
this flensverbindingdeze flensverbinding
that flensverbindingdie flensverbinding
our flensverbindingonze flensverbinding
your flensverbindingjouw flensverbinding
every flensverbindingelke flensverbinding
which flensverbinding?welke flensverbinding?
a big flensverbinding / the big flensverbindingeen grote flensverbinding, de grote flensverbinding