Quick release skewer

On the negative side, a quick-release hub renders a wheel more vulnerable to theft and care must be taken to ensure that the mechanism is properly tightened.

Similar quick-release mechanisms are also used to operate seatpost clamps, and the collapsing stem of folding bicycles and kick scooters.

According to Sheldon Brown (bicycle mechanic), manufacturers often encumber fork ends with additional hardware features meant to retain the wheel even if it is not installed properly.

[6] These secondary rentention systems in front, and vertical dropouts in the rear, while cheaper to manufacture, are less secure than traditional skewers.

[7][8] Mountain bikers often prefer to point the lever backwards, to reduce the risk of it catching on undergrowth and being pulled open.

Quick release skewer, removed from a hub, in the closed position
Hub with its skewer mounted
Quick release clamp on a seatpost
Locking skewers use specially-shaped nut/bolt to protect various parts of a bicycle