Clear acrylic lid for scientific testing apparatus with threaded ports

We use clear acrylic sometimes on top of scientific devices we design and build so they can be used as viewing ports.
On this one we have machined some ports to take special sensors and due to the lid only being 5mm thick we have to machined a 12mm thick spacer and glued it to the lid so we could machine the 3/4″ BSP thread through for the fitting.