McMaster 91611A213 Slotted Spring Pin, Pack of 100, Spring Steel, 4mm Diameter × 30mm Long, for 4-4.2mm Hole

Squeeze these pins into holes and they expand slightly, creating tension to hold parts in place. They are often used as hinge pins and as fasteners for springs and power transmission components. An alternative to dowel pins, they're lighter in weight with a hollow center and don't need a precise hole. Also known as roll pins.

Spring Steel — These pins won't deform from stress and vibration. Although they're stronger than stainless steel, they're best for dry environments since moisture will cause them to rust.