Note:
(a) The article mentions "World War II five inch rocket (as was the original Sidewinder Air-to-Air missile)."
(i) 5-Inch Forward Firing Aircraft Rocket http://en.wikipedia.org/wiki/5-I ... ing_Aircraft_Rocket
(FFAR; Diameter Warhead 5 inches; A 5-inch anti-aircraft shell was attached to the 3.5-inch rocket motor, creating the 5-Inch FFAR, which entered service in December 1943)
(ii) High Velocity Aircraft Rocket http://en.wikipedia.org/wiki/High_Velocity_Aircraft_Rocket
("an American unguided rocket developed during World War II to attack targets on the ground from aircraft. It saw extensive use both during World War II and during the Korean War"; "designed as an improvement on the Forward firing aircraft rocket or FFAR, which was underpowered and not fast enough for many uses"; Produced 1944-1955; Diameter 5 inches (130 mm))
(iii) AIM-9 Sidewinder http://en.wikipedia.org/wiki/AIM-9_Sidewinder
(Diameter 5 in (127.0 mm))
That is the measure nowadays. The original Sidewinder was AIM-9A, whose diameter I can not find in the Web.