Attached are two images of the front and back of my Mamiya TLR pinhole lenses - I hope that this answers your question.

Both use a 1/16" thick piece of oak for the plate (just because I had it around.) The pinholes were bought ready-made and are secures with gaffer's tape. The plate on the left has about 10mm of rise. Both use a much larger pinhole for the upper lens - it helps with framing a TINY bit if the sun is very bright and the subject very contrasty.