This paper addresses the issue of over-constrained assembly in mechanical designs using hole-pin patterns. When two hole-pin pairs are used, they can cause interference between components, leading to assembly failures. To mitigate this, designers often enlarge holes relative to pins to have a large float. However, when functional requirements do not permit significant float, field design engineers tend to add more assembly features, hoping them to mutually limit the float allowed by others. This numerical study employed two commercial tolerance analysis programs to demonstrate that these design changes could not sufficiently reduce float to justify added costs. Instead, this paper proposed an exactly-constrained design by replacing one of the holes with an elongated hole. Numerical analysis showed that this approach significantly reduced float compared to current design practices. This paper logically explains why this must be the case. It is hoped that this study contributes to the advancement of mechanical assembly design practices by adopting the exact constraint concep.