I just received a new stem from Specialized and it came with 3 shims and 3 top caps.

One of the shims has the center hole concentric with its outside diameter, the second has the center hole at a 2º angle with the outside diameter, and the third has its center hole at a 4º angle with the outside diameter. In the case of the second and third shims, the angle of the center hole, which fits over the steerer tube, to the outside diameter of the shim, which fits into the stem, is the key. The shim can be installed in either of two rotational positions which tilts the stem either upward or downward from the 12º position.

Using the first shim, the stem angle would be 12º if the stem is turned up, and -12º if it's turned down. Using the second shim, the stem could be installed at angles of 14º or 10º if the stem is turned up, or -10º or -14º if it's turned down. With the third shim, the range of angles is 16º or 8º, or -8º or -16º.

Regarding the 3 caps: there's one to use with each of the three shims. Two of them have the center bolt hole offset relative to the diameter that seats in the stem to center the bolt hole with the end of the steerer.

So the stem could be installed with angles of 16º, 14º, 12º, 10º, or 8º with the stem turned up or, with the stem flipped, the angles could be -8º, -10º, -12º, -14º, or -16º. All of these angles are relative to the steerer tube angle, of course. With a head tube angle of 73º, the stem angle could vary, relative to the ground, from 1º to 33º.

Wow, that's pretty wordy, but I hope it explains the adjustability situation.

Regards,
Bob P.