Named after the "Candle Stick" one can see how this piece got it's nickname. Like the CD 317 Chambers, this piece too was believed to have been used in a lightning rod installation. The groove is similar in size to the groove on a regular CD 317, except this piece has the Twiggs patented groove, making installation and replacement of the thick copper ground wire easier.
Look at [id=87142686;this picture] for the actual photograph of the recent find of a dozen Twiggs. Some patent information about them is also included which is available at the NIA web site.