De or het indexkoppeling?

The correct Dutch article is:

de indexkoppeling

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

How to use indexkoppeling

the indexkoppelingde indexkoppeling
this indexkoppelingdeze indexkoppeling
that indexkoppelingdie indexkoppeling
our indexkoppelingonze indexkoppeling
your indexkoppelingjouw indexkoppeling
every indexkoppelingelke indexkoppeling
which indexkoppeling?welke indexkoppeling?
a big indexkoppeling / the big indexkoppelingeen grote indexkoppeling, de grote indexkoppeling