That looks like a threaded headset to me. Are you changing forks to a threadless 1inch fork? Or, do you just want to mount a threadless stem on your current threaded fork. If the latter, you just need one of the many threaded to threadless adaptors made by Profile, Origin 8, Delta, and others, most for less than $15. Probably the prettiest one is sold by Velo Orange. Any 1 1/8 inch threadless stem will fit on the top portion of the adaptor. Then, the adaptor fits into your threaded steerer and tightens with a wedge, just like a traditional quill stem. Switching to a 1 inch threadless fork will require a threadless headset, spacers, and a stem, in addition to the new fork.
CC