Possibly Kluson Chicago manufacture. There wasn't a whole lot of demand for cheap American made acoustic arch top jazz boxes after the '60s so most accumulations of parts like this that we find are pre-'70s. Measured from the inside the longest portion where the slot is 1&5/8". The angled portion is at about a 45 degree angle and measures about 3/4". The portion with the mounting hole is around 9/16".