if he was wanting to change from quill to threadless that adapter would do. but its the other way around hence 1" steerer,headset and threads would be requiredNo need for a new headset etc., just fit a quill/ahead adapter, like this.
Like this. This is what I did with my old Raleigh. It has the same adapter as pointed to by Poacher, and is only a few minutes job to fit the whole assembly. I may one day fit some aero levers.
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have i read the OP wrong
If you have a threadless headset/forks/stem, then your headset width will be 1 1/8th of an inch. Typically threaded headsets and quill stems are 1 inch.
So you need to replace you forks with some threaded 1 1/8 inch forks. Your headset with a threaded 1 1/8 inch headset. You will then probably need and adapter or shim so your quill stem will fit. like this
That's a lot of bother. A simpler way, i know not.