Cracks have been found in nine heavy duty nuts used to secure the steel ropes holding up the Forth Road Bridge.
The nuts have been sent for design fault testing at a laboratory after the discovery was made during a routine inspection on the structure.
Nine of 1,888 similar nuts on the bridge were found to have cracked.
The news came as it emerged that the cost of replacing the main expansion joints in the bridge's roadway had risen by £5m to £13.7m.
Meanwhile, dehumidification equipment has also been installed on the west cable.
"Thanks to the vigilance of our inspection team the problem has been identified at an early stage"
Four nuts on that cable have already been replaced and the remaining five will be replaced over the coming year.
Consulting engineers Faber Maunsell have been appointed to investigate the cause of the cracked nuts.
Their investigation is set to include laboratory testing and a study of other suspension bridges throughout the world.
Barry Colford, chief engineer and bridge master at the Forth Road Bridge, said the bridge remained perfectly safe.
He said: "Thanks to the vigilance of our inspection team the problem has been identified at an early stage and we're already taking steps to replace the damaged nuts and investigate whether any further action is required."
Meanwhile, a new report to the Forth Estuary Transport Authority (Feta) recommends appointing Balfour Beatty Civil Engineering of Edinburgh as preferred bidder to carry out the scheduled replacement of the Forth Road Bridge's main expansion joints next year.
In the report, Mr Colford proposes further discussions with the Scottish Government to determine the most suitable way of dealing with the £5m increased cost.
Traffic disruption
Feta has been funded directly by the Scottish Government since tolls were abolished earlier this year.
A three-year settlement was agreed based on the Forth Road Bridge's long-term plan of major capital works.
The expansion joints work is due to be carried out in two phases of 10 weeks in Autumn 2009 and Spring 2010.
In order to minimise disruption to traffic, engineers plan to construct temporary "mini-bridges" on the surface of the Forth Road Bridge to lift traffic up and over the work areas while replacement is carried out.
That means that two lanes in each direction will remain open throughout most of the works.
However, four-day carriageway closures will still be required in order to construct and dismantle the temporary bridges at the start and finish of each phase. Only one lane will be open in each direction during the works.
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