As noted above, it can be possible to thread a 1" threadless steel steerer - but only if the 1" threadless steerer has the same inner diameter as a threaded steerer (22.2 mm).

Can I use a threadless stem on a threaded fork?

You can install a threadless headset on a threaded fork, if the fork steerer is tall enough and you use a quill stem. The threads should end above the headset top race. Use two locknuts tightened against each other to hold down the threadless top race, plus spacers as needed.

What is the difference between threaded and non threaded forks?

The threaded headset has recently been replaced by the threadless headset on better quality bicycles for several reasons: ... A threadless headset and fork is marginally lighter than an equivalent threaded headset and fork. A threadless stem is more rigidly attached to the forks, giving improved rigidity at the handlebars.