F1 [left] meets F2 [right]
F1-rearPanzerkampfwagen IV Ausf. F
The two maintenance hatches on the glacis plate that provided access to the steering brakes were now each equipped with a ventilator cowl made of armor steel. The fighting weight had increased to 22.3 tons.
The front wall of the superstructure now ran straight across the tank. A "Fahrersehklappe 50" driver's visor was mounted on the left, the "Kugelblende 50" MG ball mount on the right, and a vision port in both sidewalls. The "Fahrersehklappe 50" consisted of a housing bolted to the front wall of the superstructure protected by a pivoting armor visor. The "KFF 2" driver's optics consisted of two double-angled periscopes with sight apertures in the superstructure front plate above the driver's visor.
The "Kugelblende 50" consisted of the ball mount itself, its cover and adapting ring. It served as the mount for an MG 34 with an armored mantle, belt feed, plus a "KZF2" periscopic gun sight.
The differences between the Ausf F1 and F2 related to the introduction of the new gun. Ammunition storage was modified to stow the larger rounds, the amount of ammunition carried was increased and the gunner's and commander's seats were changed to allow more room. The elevation mechanism was modified and an auxiliary hand traverse was installed for the loader. Because of the long barrel, a coil-spring counter-balance was installed for the 7.5cm KwK40.
The F2 and the G were basically the same - the designation for the 7. Serie Pzkpfw IV with 7.7cm L/43 changed from F2 to G on 5th June 1942. From 1st July 1942, Wa Pruef 6 decreed that the old F1 was to be called the F and the old F2 was to be called the G.
The muzzle brake was just one of many non-diagnostic changes in production, like hull side doors in Pzkpfw III.
The F2 is basically an early G, so to speak. The F2 only existed from March 1942 until July 1942 when all F2's were renamed G's, from then on it was known as a G model. There really is no difference between an F2 and a G, since they are the same tank. The thing is, that there were modifications made during the production run.
The muzzle brakes are NOT how you tell the difference, since the G models had the single chamber muzzle brake until September 1942, when it was replaced by the double chamber muzzle brake. Likewise, the L/43 and L/48 guns are NOT how you tell the difference either, since the G model did not get the L/48 gun until April 1943.
Best way to look at it, is that the F2 and early G's are the same (since the F2 was renamed G anyway), then you have a line of G's with several modifications added, then in May of 1943, the H model comes out.