On federal work this falls under FAR 11.105, "Items Peculiar to One Manufacturer," which requires the agency to document, in writing, why no other product will meet the actual need before it can restrict a specification to one source. State and local agencies typically mirror this with their own justification and disclosure requirements, and many require the sole-source designation to be published with a window for another vendor to object before it stands. Sole source sits at the far end of a spectrum from approved equal (fully competitive) and basis of design (defaults to one product but leaves the door open) — it's the version where the door is closed by design, not by default. Sole-source language is one of the more useful things to catch early in project qualification, because it usually signals the commercial outcome is already decided. Nonlinear flags sole-source and brand-restriction clauses as it reads a bid package, so a contractor or supplier isn't spending estimating hours chasing a bid that was never really open — or, for the manufacturer already named, so they know exactly where they're protected.
Knowledge Base
What is a sole-source specification?
A sole-source specification names one manufacturer's product and gives contractors no path to substitute — used when only one product can genuinely meet a documented need, and treated as the least competitive way to describe what an agency wants to buy.
