OK, this is the first I've seen of any type of attachment bracket for the saddle block LRIs. The shank is solid iron. Possibly designed to fit in a brick mortar joint? Is this a standard type bracket, or something out of the ordinary? Any other block bracket pics out there?
UPDATE: Thanks to Spencer & Todd Grueninger, the following information along with a photo of this same, exact insulator and bracket was found in an early Milholland edition of Most about Glass Insulators. This insulator was obtained with the purchase of the Milholland collection, so there's no doubt it's the one pictured in their book.
The text reads: "St. Mary's Catholic Church, Edgefield, S.C. was built in 1858-1860. The record book, in the long account dated Dec. 18, 1860 lists as one item of expense a "Lightning Rod" at $33.60. This rod, which ran from the tower cross to the ground, was secured to the granite cross and tower walls by seven wrought iron brackets with glass insulators and tie wires. This sand blasted specimen contributed by Father Eugene Condon, an avid insulator collector, residing at Edgefield, S.C."
So there you have it! And it was once owned by our good friend, Gene Condon, one of the hobby's pioneers and a longtime LRI collector.