I have a 40mm Leupold with AO. I plan to instal a lense shade. How do I tell if it is pre 2004, or 2004 and later? The inside of the front "bell" appears to have threads.

A 2004 model will have the letter M at the end of the serial number. The letters I,O,and Q were not used.
From 74 up to 92 the letters were at the front of the serial no. starting with E(74) and ending with Z(92).
From 93 up to present the letters are at the end of the serial no. A(93)to R(07). M(04)

til later

Thanks, it looks like one is a 2004 and the other is a 2005.