The different weapon packages represent different models.
From wikipedia so take it for what it's worth:
I-16 Type 1
    Pre-production series, M-22 engine with 358 kW (480 hp).
I-16 Type 4
    First production version, M-22 engine.
I-16 Type 5
    Type 4 with a streamlined and tapered engine cowling, Shvetsov M-25 engine with 522 kW (700 hp).
I-16 Type 6
    M-25A engine, 545 kW (730 hp).
I-16 Type 10
    Four ShKAS machine guns (two synchronized in the fuselage and two in the wings), windscreen replaced the sliding canopy, could be fitted with retractable skis for winter operations, M-25B engine with 560 kW (750 hp). Hispano-Suiza-built aircraft were powered by the Wright Cyclone R-1820-F-54 engine.
I-16 Type 17
    Type 10 with two ShKAS machine guns and two ShVAK cannon, rubber tail wheel, M-25V engine with 560 kW (750 hp). Some aircraft were fitted with an additional 12.7 mm (0.5 in) Berezin UB machine gun for strafing.
I-16 Type 18
    Type 10 with Shvetsov M-62 engine producing 620 kW (830 hp), with a two-speed supercharger and a variable-pitch propeller. Capable of carrying two 100 l (26 US gal) underwing fuel tanks.
I-16 Type 20
    Four ShKAS, first version capable of carrying underwing fuel tanks with 93 l (25 US gal) capacity based on tanks used on the Japanese Nakajima Ki-27, 80 built.[citation needed]
I-16 Type 24
    Four ShKAS, landing flaps replaced drooping ailerons, tailwheel added, second cockpit door added on the starboard side, Shvetsov M-63 engine with 670 kW (900 hp).
I-16 Type 27
    Type 17 with an M-62 engine.
I-16 Type 28
    Type 24 with two ShKAS and two ShVAK.
I-16 Type 29
    Two synchronized ShKAS in the nose and a single 12.7 mm (0.50 in) UBS in the bottom of the fuselage, no wing guns. Could carry 4-6 RS-82 rockets.
I-16 Type 30
    Re-entered production in 1941-42, M-63 engine.