This is a large foot which will raise the printer 1.25" to allow for fan modifications where the fan hangs down below the printer. The pad fits over the existing rubber pads with a snug fit.
An optional pad can be printed from TPU or other flexible filament to provide some non slip grip.
It may fit on original Ender 3 but I cannot test it.
Should print fine with whatever slicer settings you typically use.
The author marked this model as their own original creation.