Learn Dutch: Gemonteerd heb ik dat spatbord nog niet. - I haven't mounted that mudguard yet.

By placing gemonteerd in the first position, the speaker is putting a strong contrastive focus on the action itself. It creates a contrast with another unspoken action, implying something like: I bought the mudguard, or I looked at it, but mounted it? No, I haven't done that yet.

Because Gemonteerd is moved to the front, why is the word order heb ik?

This is the strict verb-second (V2) rule in action. Because the fronted past participle (gemonteerd) takes up the first slot in the sentence, the conjugated auxiliary verb (heb) must take the second slot. The subject (ik) is then pushed to the third position.

Where does nog niet usually go when a sentence is inverted like this?

Even with the fronting, the rest of the sentence follows standard rules. After the inverted verb (heb) and subject (ik), specific direct objects like dat spatbord come before negations and time words. Therefore, nog niet naturally sits at the end here.

What is a spatbord, and in what situations do you use the verb monteren?

A spatbord is a mudguard or fender (literally splash board), a word you will hear constantly in Dutch bicycle culture. The verb monteren means to assemble, mount, or install. It is used for mechanical parts, putting together furniture, and even editing film or video.