Yes if you turn the brush sideways to go between the bars, no problem.
One word of caution with these. If you use and angle adapter or anything with a metal screw near the top, tape over it. Anything sharp will take the paint off the railings and make a right mess. These are usually galvanised and painted after.
The paint comes off very easy. One more thing, make sure your cones/clamps are tight. If your pole lets the brush turn when it's behind the bars, you get a hell of a job getting your brush out. Dai