I'm happy to report that this is the lightbulb I've been looking for! I bought inserts/adapters that didn't work. As soon as it arrived I put it in my 1940's floor lamp, plugged it in and luckily it worked again for the first time in 10 years. I turned down other similar lamps at thrift stores and estate sales because they needed this particular lamp. No more need. I will buy a few extra just as backups.