Some Giant Mountain bikes use the OD2 steerer-tube stem diameter. This is 1.25", or 31.8mm.
Giant sells stems, but they only go down to 60mm. While I have one on order, I got impatient waiting for it, and so designed this to see what 50mm feels like.
Warning: A bike stem is a high-stressed part. This part was made extra thick to be strong, but depending on how you print it, it may break, and that could lead to injury or death. So you have to decide on your own if you are willing to use this. I recommend just buying the real Giant 60mm part for $40. I made this just to try to see what 50mm feels like.
I rode mine no problem:
Strength depends on printing parameters and orientation.
I printed it in eSUN PET-G with 100% infill. Orient the front plate part sideways as that has good layer strength and will make the most accurate profile for the bars.
I printed the stem itself in the orientation that it sits on the bike. This gives good surface finish to the visible parts, and has a reasonable layer strength orientation.
This requires six 30mm M5 socket-cap screws, six M5 washers, six four M5 nuts.
You may want to glue some sandpaper to a 1.25 inch wood or 3D printed dowel and clean up the surfaces.