A small South Carolina parts supplier collected about $20.5 million over six years from the Pentagon for fraudulent shipping costs, including $998,798 for sending two 19-cent washers to an Army base in Texas, American officials said.

The company also billed and was paid $455,009 to ship three machine screws costing $1.31 each to Marines in Habbaniyah, Iraq, and $293,451 to ship an 89-cent split washer to Patrick Air Force Base in Cape Canaveral, Florida, Pentagon records show. The owners of C&D Distributors in Lexington, S.C. — twin sisters — exploited a flaw in an automated Defense Department purchasing system: bills for shipping to combat areas or American bases that were labeled “priority” were usually paid automatically, Cynthia Stroot, a Pentagon investigator, said.

C&D and two of its officials were barred in December from receiving federal contracts. Yesterday, a federal judge in Columbia, S.C., accepted the guilty plea of the company and one sister, Charlene Corley, to one count of conspiracy to commit wire fraud and one count of conspiracy to launder money, Assistant U.S. Attorney Kevin McDonald said. Corley, 46, was fined $750,000. She faces a maximum prison sentence of 20 years on each count and will be sentenced soon, Mr. McDonald said in a telephone interview from Columbia. Ms. Stroot said her sibling died last year.

Corley didn’t immediately return a phone message left on her answering machine at her office in Lexington. Her attorney, Gregory Harris, didn’t immediately return a phone call placed to his office in Columbia.

C&D’s fraudulent billing started in 2000, Ms. Stroot, the Defense Criminal Investigative Service’s chief agent in Raleigh, N.C., said in an interview. “As time went on, they got more aggressive in the amounts they put in.” The price the military paid for each item shipped rarely reached $100 and totaled just $68,000 over the six years in contrast to the $20.5 million paid for shipping, she said.

“The majority, if not all of these parts, were going to high-priority, conflict areas — that’s why they got paid,” Ms. Stroot said. If the item was earmarked “priority,” destined for the military in Iraq, Afghanistan, or certain other locations, “there was no oversight.”

The scheme unraveled in September after a purchasing agent noticed a bill for shipping two more 19-cent washers: $969,000. That order was rejected and a review turned up the $998,798 payment earlier that month for shipping two 19-cent washers to Fort Bliss, Texas, Ms. Stroot said.

The Pentagon’s Defense Logistics Agency orders millions of parts a year.