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In order to test the performance of algorithms for solving Constraint Satisfaction Problems (CSPs), we must establish a large collection of CSP instances that meet a given set of specifications, such as the number of variables, domain size, constraint density, tightness, etc. The goal of this report is to describe a generator of instances that have a specified degree of interchangeability. An example of such a generator is described in (Freuder and Sabin 1997), which generates non-reflexive constraints and does not allow us to control concurrently the degree of interchangeability and tightness. We have developed a technique and written a program in the C language to generate CSP instances that satisfy the above two conditions at the same time. Our generator removes the restrictions of the generator of (Freuder and Sabin 1997) and yields more general constraints. This paper presents an overview of our technique and our implementation.