I made and fitted a splitter today it’s a variation on the gutter theme. I actually used some 4in drain pipe slightly stiffer I was concerned guttering would deform with the wind pressure the blade is held by a shaped piece of galvanised plate 1.5mm which is in turn held by five 6mm set screws up into rivnuts the blade itself is slotted so should it foul on whatever it can slide from under the plate hopefully causing no body damage. The advantage of this design is that if it gets caught it only pulls out from the plate rather than damaging the car bodywork.