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If the bike came with a 1" quill stem, then it has a 1" threaded fork and a 1" threaded headset. Unfortunately, you cannot put a 1-1/8" threadless fork on it as the bike's headtube is designed to accept a 1" steerer.

However, there are still some 1" threadless forks available like this one: RST Gila T6 80mm Fork Black with 1" threadless steerer (Amazon). But you have to buy a 1" threadless headset, and a shim/adapter for current threadless stems for 1" steerers.

Or as Homebre01 suggested, get a quill stem adapter so that you can use a modern stem on it.