1-1/4 inch in diameter. Hole size is wrong, wrong wrong!
Nominal 1-1/4" fits fairly loosely into actual measured 1-1/4" hole. It will not "click" or stay in a hole in a .030" sheet metal. Very disappointing. Careful measurement of this fork: Head: 1-3/8" (35mm). Shaft: Just over 1-1/8" (B > 29mm).