On the starboard side of the rudder, the underside of both elevators, the underside of both ailerons and flaps...on the inside of the main landing gear cover... is the tiny serial stencil of the aircraft.

The Nakajima style is slightly different from the Mitsubishi style stencil in both the style font and the arrangement of information.

Here are two samples shown on the bottom of the elevators. The first is the single line "Mitsubishi" and the second is the two line "Nakajima":





Here is a sample of the starboard side of the canted rudder on EI-116... what is the manufacturer? Yes, hard to see yet it IS there! Figure out the manufacturer before scrolling to the answer...



The photo of EI-116 was made in the Battle of Santa Cruz in late October 1942. The tail code is applied to a Nakajima built Zero. EI-116 replaced another EI-116 which served in the first few months of the war. The way to determine the differences is that this Oct 42 plane had the added red piping around the fuselage stripe and it had yellow IFF stripes.