My understanding is that RH-5 is a particular design of split rim. Some people consider them particularly dangerous.
A couple of links from stovebolt.com:
http://www.stovebolt.com/techtips/wh...dd_catalog.jpg
http://www.stovebolt.com/techtips/wheels/
http://www.stovebolt.com/ubbthreads/...&Number=632556
I have seen negative comments on the safety of the RH-5 design (compared to other two or three part rims that are reasonably safe if properly treated) in several other places as well.