Here's a cool low-voltage Line Materials (L-M) lightning arrester. It was designed for 600V or less and their typical use was along RR signal lines. embossed: LINE MATERIAL CO. PROTECTIVE GAP (front) LM inside a triangle surrounded by a circle 9 (reverse). Made in clear glass with original copper mounting cap and bracket with pair of loose washers inside. Measures 3 inches tall x 1 3/4 inches wide. No chips or cracks.

First email gets this unusual lightning arrestor for only $50 plus shipping. Thanks

Updated info provided courtesy Joe Maurath Jr and Alan Norris. Thanks guys!