It's impossible to tell without an image (if you have one, post a copy
that's under 100k at
news://msnews.microsoft.com/microsoft.public.pocketpc.binaries

In the mean time, it's probably a common swivel button clip which can be
found at most electronic stores such as Best Buy or online.  Possibly

http://www.data-nation.com/index.asp?redirect=ultraclip.asp

The main difference between the version is the button design such as
diameter and the newer ones have slots to allow insertion at one angle
and prevent removal at any other angle... note the difference in the
slot width and hole diameter in the picture at the above site.

Beverly Howard [MS MVP-Mobile Devices]