In the center lengthwise these are 4.3" on the outside and 3.6" on the inside 90BOOT IF YOU HAVE A 1978 OR 1979 CLICK ON THE RING PICTURE BELOW @ SPACER CARB INLET OPENING EXTENDER FITS 30MM TO 37MM OD CARB MOUTH'S 1/17P (CARB/ADP/EXT) (S1383)MADE OF GAS RESISTANT RUBBER, THIS WILL EXTEND AND OR ENLARGE THE CARB MOUTH ON CARBS OF APPROX 33MM TO 37MM REAR OPENINGS/MOUTHS CARB/ADP/EXT (S1383)