burr n1 Also sp bur
[. . .]
4 A nut for a bolt. [EDD bur(r sb. 7 “The nut of a screw or bolt; a piece of iron or wood to protect the screw or bolt”; cf OED3 burr n.1 3 “A washer placed on the small end of a rivet before the end is swaged down”; 1661→] chiefly Inland Nth old-fash
1823 Amer. Farmer 5.2 DC, [There is] a countersink on each side, whilst one forms a rest for the toe of the leg iron, the other protects the burr of the screw, by which it is fastened on, from wearing. 1845 Ft. Wayne Times & People’s Press (IN) [15 Feb 3]/5, [Advt:] Hardware. . . Burs and Bolts. 1869 Indianapolis Jrl. (IN) 3 Dec 2/3, The new iron bridge across the St. Joseph river at Constantine, Mich., . . fell into the river on the morning of the 24th inst. Many of the burrs and bolts had been tightened a few hours before, and a change of temperature in the night caused the disaster. 1891 in 2017 (acc) Lexis–Nexis Legal Research State Case Law: PA (Internet) nePA, The superintendent of the company had knowledge of the fact that the braces needed tightening by bolts and burrs. 1892 Ibid: NY cwNY, The two circular saws were fastened to the timbers of the building by screw-bolts with burs. 1917 Sandusky Star–Jrl. (OH) 31 May 2/6, [Advt:] Steel Hose Reel—Made without burrs or bolts to loosen up. 1931 Greeley Daily Tribune & Greeley Republican (CO) 30 May 1/7, After the wreck, the burrs, the bolts from which they had been removed, and the fish plates were found lying together on one side of the track. 1962 Eve. Tribune (Albert Lea MN) 8 Mar 8/7, [Advt:] 45 jars of assorted burrs, bolts, washers and others. 1980 DARE File nwIA, SD, The word “burr” is regularly used for the nut screwed on a bolt. 1982 Smithsonian Letters IN (as of 1920s), Nuts and bolts are a common term now but when I was a boy the “nut” was called a “burr.” 1982 DARE File csWI [Service Station Operator], “Burr” is an old-time name for a nut. 1986 Gazette (Cedar Rapids IA) 30 Mar sec E 8/3, [Advt:] Box and open end wrenches; Lots of bolts, burrs and nails. 1999 DARE File WI, One of my students . . says his grandfather (a Wisconsin farmer) uses the term “burr” to describe what I would call a nut, as in nuts and bolts.