Two companies that I know off the top of my head make these: Hubbell in the USA and Codelca in Colombia.
I've seen them used for hot water heaters, some air conditioners and small electric stoves (anything that has to be connected across two 120 hot conductors for 240 volts).
But the proper (in my opinon) plug for that use would either be a 6-20 or a 6-15 grounded cap. So why use this item pictured? (photo from Codelca)
Hubbell's catalog lists it as a Nema 2-20 configuration.
[This message has been edited by SvenNYC (edited 11-07-2002).]