57-12143106 transition boot from 3.25x10 to 6" round 

Ventline Range hood vents 

Normal Stock Item

The 57‑12143106 is a galvanized steel transition boot used to adapt a 3.25" × 10" rectangular duct (common for range hoods and mobile‑home kitchen vents) to a 6" round duct for standard rigid or flex ducting.

This is the exact style used on Ventline, Broan, Range Hood, and mobile‑home kitchen exhaust installations.