A slotted spring pin is a headless hollow cylindrical tube having a longitudinal slot down the entire length with chamfered or round ends to aid installation.  This type of pin is produced to a controlled outside diameter slightly greater than the hole in which it will be installed.  Compressed as it is installed, the pin applies continuous pressure towards the sides of the hole wall.  The pressure provides tension in a radial manner to prevent loosening created by vibration or shock.