25.4 mm 120 deg Threaded 21.1 Quill Bicycle Stems
Bar clamp diameter is the diamater of the handlebar.
Stem angles are measured perpendicular to the clamp. For example, a 90 degree stem is straight. Sometimes, this may also be refered to as a 0 degree stem. If two measurements are listed, the stem can be flipped for angling up or down.
S.H.I.S clamp diameter is the steerer tube diameter.