Ed shares this 323 style mini quick release adapter find. This small version states to be a replica based on the Manfrotto 323 mini quick release adapter (found here), but comes in at less than half the price.
This mini black 323 replica made mostly of Aluminum-alloy could be a cheap solution for getting your cameras in and out of cages, jibs, sliders, etc. [Thanks Ed].
The adapter specs state it has a 3/8" threaded hole, but can be stepped down using a 3/8-1/4 reducer bushing.
[Update] Here's a review that shows the auction details were improperly listed. http://cheesycam.com/323-style-mini-quick-release-fail/. Might want to to contact the seller if you grabbed a few about this to see how you can resolve the problem.
You can find these 323 Replicas following the link (click here).
323 Replica Style Mini Quick Release Adapter