What's the difference between a lay-in diffuser and a surface-mount grille?

Lay-In Diffuser (T-Bar): Designed specifically to sit loosely inside the horizontal tracks of a standard 2\text{ ft} \times 2\text{ ft} or 2\text{ ft} \times 4\text{ ft} acoustic drop-ceiling grid framework. It requires no screws to mount. Surface-Mount Grille: Features a perimeter metal border with pre-punched screw holes. It is designed to be screwed directly into a finished drywall ("hard-lid") surface, wall, or structured bulk-head framing.

[' Lay-In Diffuser (T-Bar): Designed specifically to sit loosely inside the horizontal tracks of a standard 2\\text{ ft} \\times 2\\text{ ft} or 2\\text{ ft} \\times 4\\text{ ft} acoustic drop-ceiling grid framework. It requires no screws to mount. Surface-Mount Grille: Features a perimeter metal border with pre-punched screw holes. It is designed to be screwed directly into a finished drywall ("hard-lid") surface, wall, or structured bulk-head framing.']

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• Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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• Lay-In Diffuser (T-Bar): Designed specifically to sit loosely inside the horizontal tracks of a standard 2\text{ ft} \times 2\text{ ft} or 2\text{ ft} \times 4\text{ ft} acoustic...

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