Metal nut

Metal nuts, also simply called as nuts are gimmicks in the Sonic the Hedgehog series. First appearing in Sonic the Hedgehog 2, metal nuts can be moved up and down along large screws to progress in the Zone.

Description
These metallic hexagon nuts similar to real-life hardware devices, are found in industrial themed Zones. They are placed on long, giant screws attached between ceilings and floors. These screws create long shafts, which lead to alternate pathways both upwards and downwards (Sometimes, the screw's lower end is found hanging above the lower pathways).

The player can hop on the metal nut on the screw to move up by running right and down by moving left. The momentum will increase if there are multiple playable characters on the same metal nut or the player uses another ability to increase the nut's movement. If the player stops or his ability's speed decreases, the metal nut will stand on that point of the screw where the player stops.

Sonic the Hedgehog 2
Metal nuts first appear in Sonic the Hedgehog 2 as one of main gimmicks in Metropolis Zone. A long screws with nuts on them create narrow vertical passages with multiple pathways set on upwards and downwards. The metal nut is usually placed at the bottom point or the top of the long screw. Usually, several sets of Spikes are set on ceilings or at the bottom side of the metal nut.

When Sonic or Tails jumps on the metal nut, they will stay in the same position once the player starts build up a momentum on it. Metal nut will start move up by pressing right or down by pressing left on. The player can Spin Jump off the metal nut and perform the Spin Dash to move metal nut faster, but the rolling speed will eventually decrease. If the player has to two playable characters on the same metal nut, the rotation speed doubles and the player moves faster to the destination. However, many long passages have Asterons on surfaces, which will start activate their self-detonation, if the player stops at that point of the passage or the metal nut has two playable characters moving on it at the same time. It is hard to avoid getting hit by Asteron's spikes on the metal nut and the player usually falls off down to the bottom of the narrow passage.

Certain narrow vertical passages have alternate pathways or wide sections below, as screws are seen having pointy ends. If the player moves the metal nut down to the pointy end, it will come off the screw and falls down to the floor. If the player moves to the highest point of the screw to the ceiling, the player gets crushed. It should be noticed, that the metal nut can also crush from below, if the playable character moves the metal nut down while another character is standing below.

Sonic Pocket Adventure
In Sonic the Hedgehog Pocket Adventure, metal nuts on screws are found at Gigantic Angel Zone along with other Metropolis Zone gimmicks. Their functionality is closely the same, although the narrow passages are more tight and the player does not get any danger to fall down easily.

Sonic Lost World
In Wii U version of Sonic Lost World, metal nuts on screws are featured only in single factory section of Frozen Factory Zone 4. Here, once the player hops on the metal nut, Sonic can easily build up momentum without any strenuous work as metal nuts have only one medium speed even if the player performs the Spin Dash. The factory section has long narrow vertical hallway with bottomless pit below with several screws. The only bare enemy in the section Sprinkler is seen dropping Rings at the mid-point of the narrow hallway. The player has to reach the top of the hallway to progress the next section by using the Cannon.

Archie Comics
In the Sonic the Hedgehog comic series and its spin-offs published by Archie Comics, Sonic finds a metal nut on long screw and uses to get to the top of the hallway in Metropolis Zone. He increases the speed of the metal nut up to the top to destroy Asterons by crushing them between the metal nut and ceiling as Sonic himself quickly gets off from it.

Trivia

 * By choosing the secret pathway in the mid-point of Metropolis Zone Act 2, there is metal nut that can be moved down to fall off the screw's pointy end. As it falls down to the lava pit, the metal nut can be found out functioning as a floating platform.
 * If the player falls off from the metal nut on the narrow vertical passage, they will respond back to their starting place, if the player moves back far away and comes back to the bottom part of the narrow vertical passage.
 * In Sonic Advance, similar types of cork gimmicks on lines are found in Angel Island Zone, except these corks move to the obliquely upward by pressing right on . However, these corks will decrease down if the player stops moving on them.