1) The OED has ‘clincher’ (1874) and ‘clench hammers’ (<i>c</i>.1850) for the tool which turned the pointed end of a driven nail, so as to make it more secure.
The following much earlier reference to an iron clencher is in a list which includes large and small iron ‘malls’: 1423 ij malleis parvis cum j clencher de ferro, York. The specialist hammers probably had one flat end and they are listed in the inventories of metal founders: 1493 j clense hammer, York
1512 Item iiij clynch hamers
1516 Item v cleynche hamers, York. A similar word, where the reference may be to the nails used, occurs in a goldsmith’s inventory: 1490 De v small lez clenches iiijd, York.