Slotted Pins have a characteristic gap and are used in holes slightly smaller than their free outside diameter. The gap allows the slotted pin to contract and fit snug to the hole.
Coiled Pins work similarly to slotted pins, however the design produces a pin that is not subject to stressing on the pin because as they are compressed the stresses are distributed equally along the coiled surfaces.
Solid Pins are designed to have a press fit with retained parts. Some solid pins have grooves or knurls.