So I am looking to buy a new front fork for a bike I am putting together. I've taken some measurements of the head tube on the frame, it's 185mm long and fits a 1 1/8" headset. So obviously I have to take those into account when I am purchasing.

My question is basically between the two types of forks which I understand are either threaded or threadless. Are these two types largely frame dependent, what I mean by that is does the frame of the bike determine which type of fork you will have to purchase or are they interchangeable so long as the headset is the right size to fit the head tube? The specs on the manufacturer website aren't clear on this matter and I cannot tell just by looking because I lack the required expertise, and while a google search reveals a lot of info on both types of forks I cannot seem to find anything on whether the two are interchangeable for frames if they fit the measurements.

The frame is a Nashbar Double-Butted Aluminium road frame #NB-RDBAF if that helps.