I just took delivery of some switchcraft jacks. They are streets ahead of any asian jacks. The washer included is split in three places in order to grip the nut and wood securely. Not badly priced either.
Here's a link to their standard jack:
http://za.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=205-5440&x=14&y=17