Right now I have a cheap Suntour threaded suspension fork with threaded headset.
Well, depends on
measurements ,
A stem which is itself 1" in diameter is in a 9/8" steerer tube .
it is 1" ID, 1_1/8" OD
a Fork that has a 1" steerer tube has a 7/8" stem in it. AKA.. 22.2 ID, 25.4 OD.