De or het pijpfitting?

The correct Dutch article is:

de pijpfitting

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

How to use pijpfitting

the pijpfittingde pijpfitting
this pijpfittingdeze pijpfitting
that pijpfittingdie pijpfitting
our pijpfittingonze pijpfitting
your pijpfittingjouw pijpfitting
every pijpfittingelke pijpfitting
which pijpfitting?welke pijpfitting?
a big pijpfitting / the big pijpfittingeen grote pijpfitting, de grote pijpfitting