CAIRO, Aug 21 (Reuters) - The Egyptian pound was stable at a central bank dollar sale on Thursday but weakened on the black market.

The central bank said it sold $37.4 million at a cut-off price of 7.1401 pounds per dollar, unchanged from its last sale on Wednesday.

The rate for the dollar sales has stayed in a very tight range since the beginning of June, after the bank allowed the pound to weaken in May. It had offered $40 million on Thursday.

On the black market, the dollar changed hands for 7.42 pounds, one market participant said, weaker than Wednesday's rate of 7.38/40.

The rates at which banks are allowed to trade dollars are determined by the results of the central bank sales, giving the bank effective control over official exchange rates.

(Reporting By Stephen Kalin, editing by John Stonestreet)