This should tell you everything you need to know about the nifty locking method that Walt Evans uses for the cowling piano hinges on his Pietenpol Air Camper. Good practice dictates that removable pins be secured lest they back out in flight, and most methods involve forming the end of the pin into a loop so a screw can be inserted to hold the pin in place. Walt's method is far simpler. And while the Pietenpol does not suffer a bit from exposed hardware such as this, the technique can also be used where the hinge pins are inside a cowling or turtledeck (two common applications), as long as the end of the pin is accessible for one to grasp. There is no need to fumble around with a screw or screwdriver.

The end of the pin is formed with a slight hook to it like so, and a hole drilled so as to line up with the end of the hooked part of the pin when it's squeezed in about 1/8" to put it in compression, holding it into the hinge...

Thanks, Walt!