This one was used for supporting AC power wiring inside a house, perhaps technically a "spool", but more of a nail (or screw) knob, part of the old fashioned "knob and tube" wiring of the 1920s and 1930s. This is about 2.5 inches tall, I'll take better measurements and post them later. Embossed MIVA // T 6 on the bottom.

There is a smaller version, the T6 bis, shown [id=144520861]