Can I use a treaded fork with a thread less stem
 

I have a fork from a old frame that I would like to use on my fixed gear. the only problem is that the steertube on the fixie is about a inch and a half shorter than The one I want to install. could I upgrade to a ahead style headste and clamp a proper sive sten to the steertube?

thanks
chris

You can if you have enough steerer length so the lower half of the ahead stem is clamping unthreaded steerer.

Depending on you, your riding style and your set-up, you probably want more than half a stem on the fork.

......or have your LBS cut new threads and chop the steerer to the correct length......

Don't count on LBS being able to cut decent threads. Seen plenty of butchered jobs.