Very hard to tell, but it may be a transistor. I have never used SMD before, so I could be wrong. I don't know how you would find the part no to that, but maybe one of the other members knows how to.
Edit: Not much luck on "Z2W" - if you can post the make and model of what you are working on, we may be able to assist you in finding a service manual.
These look like SOT23 packages. We have 1n4148 signal diodes at work in these packages. One has a single diode, the other is a dual package. As mentioned, transistors are a possibility too.