C-40 said:Most brands seem to have given up on half sizes. You should know however, that a 120mm x 90 degree stem has a horizontal extension of 115mm. Unfortunately, there are also very few 90 degree stems made anymore.
An 84 degree is now one of the most common angles. A 120mm x 84 degree stem has a horizontal projection of 118mm.
Also keep in mind the change in reach due to moving the stem up and down on the steering tube. Each 1cm a stem is moved down, makes a 3mm increase in the reach.
Personally, I'd either buy a longer or shorter stem and try making up the difference with saddle movement. After years of experimentation, I've found that I can pedal with equal effectiveness within at least a 5mm range of saddle position. If you move the saddle back you'll emphasize torque and if you move it forward, you'll emphasize cadence. Since I'm climbing a lot these days, I have my saddle nearly 20mm further back than I used to, with a 10mm shorter stem and bars with 15mm less reach.