Where one, who in fact is a surety on a contract, by express terms binds himself as a principal, by naming himself as a principal, he will be liable as such, and he can claim none of the rights of a surety. By signing as principal to the obligation, he waives the rights and privileges he might have claimed by making his contract one of suretyship only.7 Where a number of parties sign a bond and all add the word principal after their names, and there is nothing to indicate that any of them are sureties, they will all be bound as principals, notwithstanding some were sureties merely; it is held also in such a case that they could not plead a defense to the contract by showing that an extension of time was given for the payment of the debt.8 It is a general rule subject to certain exceptions that sureties are estopped to deny the facts stated in their contract.8