Fits units that are 45-mm X 26-mm by 14-mm deep. Designed to make it more easily mounted to flexible, thin panels. Mine is mounted to a 2-gallon bucket lid to serve as a monitor for dry storage for filament. Bucket lid shown is 1.5-mm thick.

I acquired these combination Hygrometer / Thermometer from Amazon

Material, layer height, and fill are all flexible. Support is not required.

The printed one shown is Hatchbox black PETG at 0.35-mm layer height 50% fill.

Hardware used is four M3X12-mm flat head Phillip's in stainless steel (92010A122) with four small pattern thin nuts in stainless steel (90710A030).  The wells for the nuts are deep enough to support material thickness up to about 3.5-mm with the 12-mm screws.

You may need to clean up the holes for the screws with a #32 or 3-mm drill bit, and possibly touch up the countersink with a 90° countersink tool.