can i put an A-Head Set on this?
 

it has a thread at the top but i dunno if that has anything to do with the headset that i can attatch to it.

Can you clarify your question? Are you replacing your headset? Is that 1 inch, or 1 1/8? If your steerer is threaded, you use a threaded headset.

its just a bare frame, it doesnt have a headset. its threaded so i guess i'll be putting on a threaded headset.

There's quite obviously at least half a headset there. There's head cups pressed into the frame.

It's probably not a good idea. Here's why: The stem clamping onto your fork's steerer tube is what actually holds a threadless headset in adjustment. With the threaded fork that you have shown, you are going to be clamping the stem onto the threaded section of the fork. That means that all of the stresses of your front end are going to be concentrated right on the single thread at the bottom of your stem. You might find yourself coasting down a hill someday and discover that your handlebar isn't connectd to anything and that your fork wants to fall out of the bottom of your frame.

Looks to me like a star nut for a threadless HS already in the steerer. Generally if the steerer is long enough that a threadless stem can clamp at least 1/2 it's height onto unthreaded steerer, it's ok.

Did you have the star fangled nut that's in there pressed in or did the fork come that way?

I can't imagine why you couldn't use a threadless setup, seeing as how you've got a star nut already in there; just get a Aheadset top cap and bolt for it.

Somebody alreay said why not depending on what the stems ends up clamping to!

There still seems to be a little confusion here......well, at least on my part. Cam0, do you already have a stem? If so, is it a threadless stem or the traditional quill type stem? If that is your frame in that photo, I'd personally stick with the traditional setup as your frame is lugged and most likely it's a 1 inch headtube.

Well he sure as heck isn't going to be able to use anything but a threadless stem without removing or pounding down that star nut jammed in there.

What exactly is the question here?

Can you put an "ahead-set" threadless headset in that frame? Sure, why not. 1", 1-1/8", makes no difference, just buy the correct size.

Can you put the rest of the existing headset on and then use a threadless stem? Sure, as long as the existing headset is threadless and you're not clamping the stem entirely on the threaded part (as sydney has said.) If it's not gripping the unthreaded portion of the stem, you risk breaking the steerer.

I think you're mixing up some terms - best to get your understanding and terminology straight before asking advice.

Yeah, makes me think someone already had a threadless setup on there, but that doesn't mean it was the smart thing to do.But bikes do suffer a lot of dumb stuff.

True, that star nut can be pounded out or simply buried down below in a few seconds.

If the steerer only has threads at the top, I see pushing the start nut down and cutting off the threads as an option, if that leaves him with enough steerer tube. The problem is that he really doesn't know what he's talking about, or how to ask what he's trying to accomplish, which leaves us guessing.

Correct observation.