De or het fietsuitrusting?

The correct Dutch article is:

de fietsuitrusting

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

How to use fietsuitrusting

the fietsuitrustingde fietsuitrusting
this fietsuitrustingdeze fietsuitrusting
that fietsuitrustingdie fietsuitrusting
our fietsuitrustingonze fietsuitrusting
your fietsuitrustingjouw fietsuitrusting
every fietsuitrustingelke fietsuitrusting
which fietsuitrusting?welke fietsuitrusting?
a big fietsuitrusting / the big fietsuitrustingeen grote fietsuitrusting, de grote fietsuitrusting