Single slit diffraction and the thermal expansion of materials are common components of an undergraduate physics course, though these topics are often taught independently in both lectures and laboratory based courses. Higher levels of cognitive domains can be achieved by building on these established topics and combining them into a single experiment that also introduces new tools and techniques for data handling and analysis. Here we describe an experiment where the thermal expansion of a metal bar shifts an attached razor blade such that the separation between this blade and another fixed blade decreases. This decrease in blade separation allows for changes in the peak separation for single slit diffraction to be measured and the expansion coefficient of three metal bars (copper, steel and aluminium) is determined to good agreement with accepted values. The use of multiple peak fitting allows students to develop more sophisticated analysis techniques that are applicable beyond this experiment and are transferable to different areas of experimental physics.