To whom it may concern, the T91 Quad Rail (https://store.t91tactical.com/T91-Quad-Rail-Handguard-Made-For-BBG-p95432957) lower half is cross-compatible with the T91 polymer handguard. Just use the provided Quad crossbolt.
The Quad upper does not fit with the polymer lower half.
The Tri-Rail sadly does not fit on this configuration.T91 Quad + Poly Handguards
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