Robin,
Yes the removal/replacement will be done by the end user, so I can't
use the dowel suggestion (although a cheap and excellent way to do it).
I'm now thinking more of the keyed male/female set (maybe just a simple
square shaped key and hole), slide it in with some type of lock-down
mechanism that doesn't effect the alignment. .5 degrees isn't extremely
precise so maybe this will work. The object is a small (2 ounce)
electronic orientation sensor and it needs to know the orientation of
it is relative to the object its attached to.

steve