De or het tunnelelement?

The correct Dutch article is:

het tunnelelement

Rule Words ending in -ment: usually het. See the rule

How to use tunnelelement

the tunnelelementhet tunnelelement
this tunnelelementdit tunnelelement
that tunnelelementdat tunnelelement
our tunnelelementons tunnelelement
your tunnelelementjouw tunnelelement
every tunnelelementelk tunnelelement
which tunnelelement?welk tunnelelement?
a big tunnelelement / the big tunnelelementeen groot tunnelelement, het grote tunnelelement