Mechanic reports he installed a new Tamdar upgrade probe without a new spacer on their Saab 340 aircraft.

Narrative

The event took place in September 2008. It was my first time doing the Tamdar upgrade. I was doing with my fellow mechanic. He showed me how to replace the probe. I took out the old probe and replaced the new probe. I thought that the new probe came with a spacer. I asked him if it did and he said that it did. So I put in the new probe; and closed up my work area. I didn't know that the new probe did not come with a spacer. The spacer was replaced at another maintenance facility. I believe this event occurred because of my lack of experience. This was my first time doing the Tamdar upgrade and I had only been with the air carrier for a couple of months. I also think miscommunication contributed to the problem. The other Mechanic and I were unclear about the spacer. To make sure you communicate with the mechanic you're with; go back and verify things and don't be afraid to ask questions about things. The dumb question is the one that you don't ask.Callback conversation with Reporter revealed the following information: Reporter stated the probe is mounted to the bottom of the fuselage with four bolts just a little to the right of centerline and aft of the nose gear. Access to attach the canon plug connector; is from a side panel. The crew oxygen bottle is also located in the same area.