1) The linch-pin or nail which secured the wheel to the axle-tree, noted from 1496 in the OED.
1485 ij lyn’ nayles, Ripon
1558 a wayne, to [sic] lyne nayles, two apiltone [suspect axiltre] nayles of iron, Castleford
1637 a gang of old wayne strokes … 2 lynnailes, Thorpe Willoughby. Note: 1580 a lynce pynne nayle, Beverley
1653 bolts, shackles, runners, three lynn-pinns, Northallerton.