The dimensions are venturi sizes, not the throttle bore size.

The Homelite 45 uses a ZAMA C1Q-H44 =14mm =.551" venturi. Zama's have no number cast in venturi inlet

The throttle bore size for theZAMA is 16mm = .630" or a little over 5/8"

The G 38 uses a Walbro WT-338 =13.49mm =.531"= #34 cast in inlet Throttle bore is 17.44mm or 11/16"

The G 45 uses a Walbro HDA48D =15.08mm =.5937"= #38 cast in inlet Throttle bore is 19mm or 3/4"

Enjoy,

Jim