1) In Old French, <i>aissellier</i> could refer to an axle: it derived from the Latin word <i>axill?ris</i>, a diminutive of ‘axis’ which also had those meanings.
It was regularly used of boards or planks: 1622 60 asshellers whereof 32 to be 4 foet 4 inches longe and 6 inches broad, Brandsby. It has had a fascinating semantic history in English but was used from an early date primarily of stone, descriptive of hewn blocks which were worked to a fine surface and closely jointed: these gave prestigious buildings an imposing façade: 1412 xx carectas lapidum, exceptis … ascheleres et flagges, York
1494 Saynt Elyn wharell ... et lapides ibidem inventos vocatos Ashlerstones, Roxby
1558 all my tymber redy to build with all my slayt stone and ashler stone, Wakefield. The earliest reference that I have noted in connection with bridges is in the mason’s contract for Apperley Bridge in 1602 which required the workman to put … as many through achlers into the stone works as the overseers shall think proper. These were bond-stones designed to strengthen the masonry. The mason John Phillip was paid the same rate in 1616 for hewing the over Arch stones as for the Ashellers, Kirkstall.