Kore Lite 3 Stem
Stems have to fit the steerer tube, for the Isis the stem diameter is 1 1/8". Most MTB stems are this diameter. Other measurements are stem angle and stem length. Stems should be replaced every 4 years or less as this part is vulnerable to material fatigue. Stems are an important component for frame fitting. I have no idea what size to get so I just picked a inexpensive stem in the mid size range. Someone suggested buying a bunch of different sized Tahoma stems to try.
Recommendation: It is likely that a number of stem sizes will need to be field tested before the "chosen one" is found. Unless you know exactly what you want, don't spend alot of money on a stem. Stems are often discounted heavily. It is not unusual to find $75 stems discounted to about $20, so shop around.
The Kore Lite 3 stem was on sale, I picked a 5 deg , 120 mm length. The most important thing was the handlebar stayed attached to the bike and the color matched my forks, hahaha.
Tip: Use lipstick and color the top surface of the headset spacer. Snug the stem up against the headset spacer. Remove the stem and check to see if the lipstick mark is even around the base of the stem clamp. I found my stem to contact only one spot one the headset spacer. Use a nail file to remove the high spots and ensure even pressure is applied to the headset top plate.