Hi Tim!
As I promised, here are a link where you can see one of the brass-porcelain sockets about you asked us another day:
http://mis-bombillas.webcindario.com/Album_E27_Lat_Por.htmDespite the fact of these lampholders are being substituted by new CE plastic models, here in Spain are nowadays being sold in almost every electric stuff store, by no more than 2? a piece (almost 2$).
I ignore both where they came from and the name of the manufacturer, but these are brand-new sockets from current manufacturing, not vintage ones. This latter can be confirmed by the visible "CE" engraved etching on outer sleeve's wall, wich means that them have passed the CEE electrical requirements.
Each one's rear cap are fitted with a Metric 10mm thread for tubing or raccord fastening and so with a little screw to secure it.
Really these are a well made lampholders, with a pristine golden shining that enhaces the look of any bulb that could be screwed in one of them. And of course, the upper ring are made of genuine porcelain!
Best regards,
M. Gonz?lez.
http://mis-bombillas.webcindario.com