IT solutions in manufacturing support the execution as well as the monitoring of production operations. Fast reaction to exceptions, detailed documentation of operations, and the detection of inefficiencies in the production are among the benefits of a tight IT integration of shop-floor processes. Several dedicated software solutions and standards exist for the manufacturing domain. However, each manufacturer must tailor the IT to the special requirements of its processes and infrastructure. We found that real-world installations show considerable variations. In this paper we present the results of seven case studies on IT infrastructures in manufacturing. For each case we portray the employed architecture and the main factor that influenced the design. From this analysis we derive reoccurring patterns on the structure of IT solutions in manufacturing and relate them to existing standards. Our results provide system architects with guidance for picking the right architectural choices in different manufacturing environments.