One way to have interchangeable pinholes and zone plates in a body cap or in a home-made camera is to mount a filter with the glass removed in the cap or camera. Another filter ring can retain a disc with the pinhole or zone plate. A third filter with opaque material substituted for the glass works as a shutter for longer exposures. A handful of old filters all the same size can be cheap online or in some camera stores.
I usually use .002" brass shim stock for pinholes. Thinner shim stock is more difficult to work with. Thicker shim stock is unnecessarily thick. For critical results, the pinhole diameter is important. I'd use about .010" for a 55mm focal length, based on testing for optimum central sharpness. A slight increase in diameter will favor off-axis sharpness. Making the pinhole large enough to significantly reduce exposure will yield awfully unsharp images.