Sarah Williams said she had no doubt they would have carried out their threat if she had not co-operated.
Mrs Williams, 68, and her husband, former Army major Tom Williams, 73, were tied up during the raid at their country home.
Mr Williams was beaten with a cosh and kicked as he lay defenceless on the ground, a court heard.
The couple were in the drawing room at Aldsworth House, near Chichester, when the security alarm was triggered by movement in the grounds outside as they watched television at 9pm on June 4, 2006.
Mrs Williams went to check outside but could see nothing and thought the alarm had been tripped by their dogs or a fox.
Minutes later the alarm went off again and Mrs Williams went to investigate.
As she opened the back door a man wearing a balaclava barged past her.
Mrs Williams told a jury at Hove Crown Court yesterday: "I screamed pointlessly but it was rather terrifying."
Two more raiders came in behind the first and ran through to the drawing room where her husband had been half asleep in a chair.
Mrs Williams said: "By the time I got there they were attacking my husband.
"One had a truncheon which he hit Tom over the head with.
The other was kicking him in the ribs.
"I tried to go towards Tom but the second man stopped me and pulled my left hand behind my back.
"He took my engagement ring off and strapped me up with gaffer tape."
Her hands, arms and feet were bound and her jacket put over her head to stop her from seeing the robbers.
She said the gang's leader demanded to know where the couple's safe and jewellery was.
Mrs Williams added: "I told them there was a safe upstairs.
"Tom told them the police were on the way and I was very worried they would attack him again.
"I heard them walking around upstairs and then they came down and asked where the proper safe was.
"We had to deny that we had another safe or jewellery and said that had all gone in a robbery in October.
"They got cross and started checking for silver.
"They found the silver and there was tremendous banging as they took the insides out of two grandfather clocks."
Mrs Williams said the raiders eventually found the main safe and demanded the keys for it.
But even then her husband remained defiant and told the robbers it was their son's safe and they did not have a key.
Mrs Williams fought back tears as she recalled: "They said they would pull Tom's fingernails out one by one if we did not tell them where the key was.
"I had no doubt they would have done it if I had not told them.
"They were clearly going to get the key to that safe, one way or another.
"I said I would tell them only if they agreed not to take my husband's collection of medals.
"They are all family medals and they are irreplaceable."
Mrs Williams showed them where the safe key was. She was then led back to the drawing room with her husband.
She added: "They all wore balaclavas and gloves but I did not look at them.
"I was so frightened they would kill my husband. The leader's voice sounded ruthless and I thought he would do what he said he was going to do."
Two of the raiders loaded antiques worth £380,000 into the Williams' car and drove off.
Walton Hornsby, prosecuting, alleges the raid was carried out by Wolfgang Schmeltz, 57, Christopher Doughty, 48, and William Johnson, 47.
Antique dealers Daniel Brummer, 56, and Christopher Capewell, 63, are accused of handling stolen property.
They are said to have received antiques stolen from country homes in Firle, near Lewes, Slinfold, near Horsham, Petworth and Bexhill.
Schmeltz, Doughty and Johnson, all from Southampton, deny robbery.
Schmeltz and Doughty have admitted one charge of conspiracy to handle stolen goods.
Capewell, of Grand Avenue, Hove, and Brummer, of Furze Hill, Hove, deny conspiracy to handle stolen goods.
The trial continues.