Navvy gravvy

[Gregory]

Unlike [Itsy Bitsy] and Teeny Weeny, [Navvy Gravvy] doesnt refer to just a small size but to a small amount. A navvy gravy is a very small amount, a little tiny bit, a very fine shaving. In common use within the Royal Dockyards where very small adjustments have to be made, by shipwrights and shipfitters, to customise components in order to get them to fit correctly. Thought to date from around the mid-nineteenth century when many tasks in [shipbuilding] were still carried out by eye, although the origins or the words themselves are not entirely clear, it is still in use today where non-standard sized items have to be adjusted to fit.
As an illustration; if a hole is drilled in a piece of metal to take a bolt, the hole is the correct size but the bolt doesnt fit. The drill is then run through the hole again and the bolt fits. Careful examination may reveal a few grains of metal dust or the tiniest finest curl of [swarf] removed by the drill, that tiny amount is a [navvy gravvy].