Anker LC40 flashlights can use either one lithium 18650 cell or an adapter holding three AAA cells. I now prefer 18650 cells, but they’re nigh onto 4 mm smaller than the flashlight ID and rattle around something awful.
I can fix that:
Three new entries appear in the cell dimension table of my OpenSCAD inter-series battery adapter program:
NAME = 0; ID = 0; // for non-cell cylinders OD = 1; LENGTH = 2; Cells = [ ["AAAA",8.3,42.5], ["AAA",10.5,44.5], ["AA",14.5,50.5], ["C",26.2,50], ["D",34.2,61.5], ["A23",10.3,28.5], ["CR123A",17.0,34.5], ["18650",18.8,65.2], ["3xAAA",21.2,56.0], ["AnkerLC40",23.0,55.0] // Flashlight tube loose-fit for 3xAAA adapter ];
I took the opportunity of adding OpenSCAD Customizer comments, which means this now works:
The model looks about the same as before, although with a few more sides just for pretty:
That was easy …
The Smell of Molten Projects in the Morning 
Why does it look metallized?
“Natural” PETG threads extrude nearly clear and the cylinder wall has no infill, so you see weird optical interactions between the perimeter layers. In person, some sections appear dead black at the proper angle.
The grayish zits scattered over the surface come from the usual end-of-perimeter pauses. Normally, I stack ’em up in a column, but this thing fit the flashlight better with distributed ugliness.
Rubber band? :)
Kapton tape wrap?
C’mon, you know me better than that! [wince]