An open beam x-ray diffraction system and method are provided including modular x-ray heads for being detachably connected to a base unit having a common drive assembly that shifts the heads in an arcuate path during an x-ray diffraction measurement operation. The heads can be tailored to different performance criteria depending on the needs of the measurement operation that is to take place. To this end, one of the heads can be a microhead that is adapted to take measurements from otherwise difficult to access surfaces, such as on the inside of tubular parts. Enhancements to the drive assembly for improved accuracy and speed are also disclosed.