Arken Zulus HD is night vison optical device - its focusin wheel is rather stiff so throw levers are widely used. This model is in one piece, requires no screws - only retaining ring of the front lens cap has to be screwed out to alow removing of the lens cap - the lever the is slided on the focusing ring, it snung nicely thans to the grooves. Aftewards, the lens cap is put back on. 

I printed with PETG 0.12 layer, 5 walls and 60% infill.