It a weird looking set up on the OCR 1 pictured in my 2003 Giant catalogue. Looking at the specs, it is indeed an 'Alloy Adjustable Quill Type' stem, with a threaded Chromoly steerer and threaded headset, but not too sure if its a 1" (22.2mm quill) or 1 1/8" (25.4mm quill) steerer. Looks to me like a 22.2mm quill (but I could be mistaken). It should be easy to loosen, pull out quill and check (size will probably be stamped on it)
You can easily find alloy quill stems with removable faceplates in either size to replace your current, original Giant one. There are some cheap, ugly, 22.2mm stems available on special for $10
here at the moment, if you're looking at not spending much (I recently bought one). Plenty of much nicer looking ones around in varying lengths and rises in bike shops and on-line
If you are thinking of changing to a
threadless/ A-head style stem
and headset, you
won't be able to, as steerer tube is too short to suit threaded steerer. You will need another fork with a longer unthreaded steerer to do this
You can, though, run a
threadless style stem with your existing headset using a number of different
quill insert adaptors. BBB make one that suits both 1" and 1 1/8" steerers and stems
Whatever you do, make sure the bar clamp size on the stem is right for your bars (more than likely 26.0/ 25.8 mm)
A bit of a strange decision for Giant to run this stem/steerer/headset combo just for the sake of an adjustable stem. A few of their 'Comfort' range that year are running 1 1/8" integrated threadless headsets with adjustable stems, but seems they couldn't find or develop one themselves to suit their OCR's in 2002/ 2003. They did get their act together in 2004, though