Spank 28.6 90 deg 50 mm Bicycle Stems
S.H.I.S clamp diameter is the steerer tube diameter.
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.
Stem length is measured from the center of one clamp to the center of the other clamp. This measurement is sometimes known as the reach or extension.