Here's a lightweight webbing reducer that shows promise. Haven't done much testing with it, however.
The photo shows a small white piece of plastic sheeting making the transition from 2" wide webbing to 3/4" wide webbing. The plastic piece is cut (with scissors) from a roll of plastic roof flashing from Home Depot. The plastic cuts and sews easily.
Why do this?
(1)It will allow me to use, in this case, a 3/4" buckle and 3/4" webbing on a waist belt that would otherwise require 2" wide buckle and web. This saves a net of 3/4+ ounces of weight (after adding back in 1/20th of an ounce for the white plastic triangle).
(2) The myog plastic triangle is lighter than available reducing buckles that I have seen.
(3) One can make any size reducer at home. A 4" wide light waist belt, for example, would fit the waist more evenly if a reducer was sewn in between the (typical) 2" wide buckle and 4" wide belt. Most waist belts I have seen aren't very tight on the top and bottom if the waist belt is wider than the buckle.