5/8 - 26 tpi Lock Nut.
NCL58026 - Q40
This is a single chamfer nut made from 303 stainless steel. It is machined back and front for a superior finish and the hexagon sides are hand finished to a semi polish. It then spends 72 hours in a polishing machine to slightly dull the sharp edges and to give them a silky feel so you do not leave cloth particles on them when cleaning the bike
You can buff it to a chrome finish or sand blast it for a cadmium look.
These nuts are in a class of their own and not like the ones turned from hexagon bar you see elsewhere.
Photo shows 2 nuts for clarity. Price is for just 1.