A bank of horizontally oriented boiler tubes which are periodically exposed to the abrasive action of a stream of blowing fluid cleaning medium. Portions of the boiler tubes, located at the top of the bank, are provided with spaced shields for protection from the fluid cleaning medium. An anti-vibration bar extends vertically between the protective shields to suppress vibration of the boiler tubes. A cap is fitted over the top end of the anti-vibration bar. The cap is sized to overlap adjacent portions of the protective shields thereby covering any gaps between the anti-vibration bar and the shields that would expose the boiler tubes to the action of the fluid cleaning medium.