An esoteric ode to that most humble and overlooked of all fasteners: the castellated nut. (This is a nut with open grooves that resemble the structure of merlons & crenels at the top of a castle wall, or turret. Castellated nuts are often used with bolts or threaded shafts that have a hole in them - one aligns the crenel with the hole, and passes a cottering pin, or such similar device, through both parts of the fastener, thus securing them from coming loose. Do not confuse castellated with knurls, which are an entirely different thing. :)