There have been several threads over the years asking if Shimano and Campy brifters, road shifters and road brake levers take the same cables. The answer is generally no and many posters have reported problems using Shimano-size cables in Campy brifters while a few claim to have had no problems.

To quantify the differences I miked the end fittings on both Campy and Shimano spec'ed road brake and shift cables and here are the results:

Brake cable end fittings:
Shimano "mushroom cap" diameter: 0.238" (6.05 mm)
Shimano "shank" diameter: 0.140" (3.56 mm)

Campy "mushroom cap" diameter: 0.214" (5.44 mm)
Shimano "shank" diameter: 0.138" (3.51 mm)

Shifter cable end fittings:
Shimano end barrel diameter: 0.173" (4.39 mm)
Campy end barrel diameter: 0.159" (4.04 mm)

Note for both brake and shifter cables Shimano end fittings are enough larger in diameter than Campy and will most likely jam if forced into place.

Lesson: use the right cable or prepare to file down Shimano fittings if you have to use them in Campy components.

I have no experience with SRAM brifters but I believe they use Shimano size cables. If anyone has actual info I'd appreciate it if they would either confirm this or post the correct dimensions.