A diffuser for the LetonPower BB27 underwater photography light from Aliexpress. Likely fits the other models and clones too. No tools needed - just clips on.
Clear PETG works best. Use a default preset for a 0.2 - 0.3mm layer height.
I printed mine from an old spool of clear DevilDesign PETG with a 0.4mm nozzle and a 0.3mm slicer preset.