Here's the measurements off mine:
OD of barrel between sight and flash suppressor: .0562"
(The barrel is thinnest here), it is 0.628" under the handguards and sight base)
OD of 3prong flash suppressor at base: 0.863"
OD of 3prong flash suppressor at end: 0.678"
Length of 3prong flash suppressor: 1.75"
OD of M16A1 flash suppressor (not shown): 0.863"
Length of M16A1 flash suppressor (not shown): 1.75"
Height of sight base from bottom of barrel: 3"
Length of sight base at bottom: 1.85"
Length of sight base at top: 0.79"
Width of sight base at bottom: 0.79"
Width of sight base at top: 0.50"
Distance between sight base and flash suppressor: 4.8"
Click here for a closeup pic of an M-16 "3 Prong" flash suppressor.
Click here for a closeup pic of an M-16A1 "Bird Cage" flash suppressor.
Mine has an AR-15 lower receiver, but that is an actual Army surplus M-16A1 upper and early M16 furniture on it.