Around 430 aluminium and copper tubes valued together at £6,000 were stolen from an engineering company in Darwen.
The crime took place on Spring Vale Road between 2pm on November 18 and 3pm on November 19 and police are now trying to establish why it took so long for the theft to be reported.
They say a vehicle would have been required to move the load.
Anyone with information is should contact Darwen CID on 01254 353841 or crimestoppers on 0800 555 111.
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