I bought a couple of those adaptor wossnames off the Mega-Global Big River Corporation of Seattle, USAnia the other week so I can use up my vast stock of small screw-fitting spotlight bulbs.
Still got a couple of bayonet-fitting CFL jobbies (freebies) waiting for when the bulb goes in the Lesser Bedchamber or the Estate Office which, at current usage rates, will be some time after my eleventy-first birthday.