I find these in my local creek. Suspected they may be insulators, been using them as display pedestals for my bottle/marble collection.
PS I do know the item treeguyfred was referring to—I had those on the last house I owned, which was built in the 20s.
Thx Robby. Recently dug a Philly mug-base Hutch rated Rare in Hutchbook, and Ron at HB said they knew examples existed, but mine was the 1st they'd seen. Seems to jibe with 20–40 known.
Planeguy2 - congrats on the pickup! There are bargains out there for sure.
Nice sheared lip, pen-rest, ink. I love this design, and have seen English mudlarks & bottle diggers find them regularly. Glasshouses churned these out in quantity (even the sheared lip was a step-saver, no tooling req'd). So there are lots out there.