Z-FLEX's Z-Vent Double Wall Adjustable Wall Thimble is for use when the vent passes through a horizontal opening, and not required for non-combustible walls.
| Vent Type: | Double Wall |
|---|---|
| Product Type: | Wall Thimble |
| Diameter (Inches): | 4" |
| Length: | 6" to 7" |
| Material: | Stainless Steel |

Hi Ric! The inside diameter of the hole would be 5.13".