Supposing it might be useful to the United States, I went to the workman; he presented me the parts of fifty locks taken to pieces, and arranged in compartments. I put several together myself, taking pieces at hazard as they came to hand, and they fitted in the most perfect manner. The advantages of this, when arms need repair, are evident.
 Thomas Jefferson to John Jay, August 30, 1785, United States Department of State, The Diplomatic Correspondence of the United States of America, (Washington: Blair & Rives, 1887), 1:642.
A reader pointed me to this letter from President Jefferson to James Monroe, November 14, 1801.
Dear Sir, —The bearer hereof is Mr. Whitney at Connecticut a mechanic of the first order of ingenuity, who invented the cotton gin now so much used in the South; he is at the head of a considerable gun manufactory in Connecticut, and furnishes the U. S. with muskets undoubtedly the best they receive. He has invented molds and machines for making all the pieces of his locks so exactly equal, that take 100 locks to pieces and mingle their parts and the hundred locks may be put together as well by taking the first pieces which come to hand. This is of importance in repairing, because out of 10 locks e.g. disabled for the want of different pieces, 9 good locks may be put together without employing a smith. Leblanc in France had invented a similar process in 1788 and had extended it to the barrel, mounting & stock. I endeavored to get the U. S. to bring him over, which he was ready for on moderate terms. I failed and I do not know what became of him, Mr. Whitney has not yet extended his improvements beyond the lock. I think it possible he might be engaged in our manufactory of Richmd. tho' I have not asked him the question. I know nothing of his moral character. He is now on his way to S. Carola. on the subject of his gin. Health & happiness cum cœteris votis.Jefferson doesn't say that he has seen this done.