A nail is a device in Chip's Challenge that allows Chip, or sometimes a block, to walk over a force floor by blocking its destination, often with a block(s) and a block-acting wall; monsters cannot cross nails, as they will be trapped as at the beginning of Just Enough. The name comes from Wormwood, which contains a long hint explaining the use of the one safe block with the buried fire boots using this term.
Mechanics and setup
Chip is allowed to override force floors in various degrees between MS and Lynx. In MS, it can be overridden if the last move was a slide or an involuntary run into any acting wall; by contrast, Chip is not allowed to override a second time in the same position after running into a wall voluntarily, as when attacking the blue walls around Ping Pong. Lynx allows the involuntary wall smash, which can include a slide back onto a force floor from ice that hit an acting wall (seen in Dancing on Ice), but otherwise all involuntary moves must be from force floors.
The setup in Wormwood initially looks like this:
Because this level is busted, there are two different solutions, but both require the basic nail as defined here: remove chip 2, then drop the block onto its location such that the wall tile turns the block into an acting wall and the suction boots can be collected. This nail is possible in Lynx, but the block is unable to reach this location because the hint is a block-acting wall in Lynx. In the no boost route, the block has its own nail function, as it must move R from this location and the chip must remain uncollected temporarily; the busted route no longer requires the block.
Monsters can be held by nail formations, but only one type usually allows them to be used later, involving a toggle wall. A simple example is Waterslide, where a glider is held behind toggle walls such that it will hit a brown button that cooks the level after two presses of a green button. The nail is used to hold the glider in place such that it will always and immediately move to the next stage. These are not nails in the traditional sense and are not counted below.
The basic nail formation has been used as a device in various levels since the release of CC1, though it is not officially used in any CC1 levels. Since getting across column 7 of the force floors in Mixed Nuts requires a 2R move at 10 m/s and it was likely to miss the teleport into the exit the first time, requiring a second pass through this section, the blocks in the room to its right (unusable anywhere else) were initially used as a safety measure (to avoid possible death by bomb) or as a guaranteed path across after seven blocks. This is no longer necessary, since death is exceedingly unlikely and if the teleport is overshot to the right, Chip can step D into it and still reach the exit.
In CCLP2, the nail is officially named by Wormwood, but it also appears in other levels. There are more examples inside bold time routes, but most of these are unnotable occurrences.
- The Headbanger Rule, if used on force floors, can provide a temporary nail, thereby busting Flame Boy; although the official ChipWiki route for Suction Ride does not include this (due to extra skill for no points gain), it is possible to use this to step on [11/14, 6] and use the boosting to reach the required distance away from the block, saving  each time.
- A backwards ice corner nail appears at the end of The Parallel Port, and a backwards clone block nail in the southern section of Sudden Death; these are not possible in Lynx.
With an increased reliance on puzzles, but also Lynx compatibility, only certain types of nails are seen in CCLP3 but are fairly common; only the major occurrences are included, where they are part of the solution. It is increasingly used in the harder levels.
- Two Sets of Rules offers a choice between two possible two-block nails, one of which is backwards and works in MS, while the other requires a red key but is the only one valid in Lynx; a basic two-block nail can bust Replay, though the solution is slower than bold.
- An idea used previously in custom level sets but never in an official set is a socket nail, first seen at the beginning of Motion Blur. Part of the puzzle in this level is to not collect enough chips to open the socket, as Chip will be trapped behind the force floor.
- A red lock nail is set up at the end of Zelgon's Lair to test window shopping; only eight red keys should be collected, as the ninth traps Chip behind the force floor, and the entire device is visible earlier in the level.
- At least a nail against a wall is necessary to solve the first room of Countdown, though a one-block nail moves Chip through the room faster.
- Both a block and Chip nail appear in Rotation, to the northeast of the start. Chip must push block 1 onto a nail created by block 3, then allow himself to pass the nail himself by adding block 2 later (as the block can pass over the force floor, but Chip will be able to push block 3 as he attempts to cross).
- The intended route to Yet Another Yet Another Puzzle pushes three blocks down the far west edge of the level, two of which create a two-block nail that accesses the blue key.
- A blue lock creates a nail in Mudpie; when approached from the east side, Chip cannot have a blue key, and when he enters the room it guards for the first time, suction boots are necessary to escape the room.
- To cross blocks over the force floor strip on row 11 of Suspended Animation, Chip must nail blocks onto one of the east force floors and push them off.
- The device for adding the final two blocks to the northeast room of Avalanche is to throw them onto the force floors, nailing the second one down until it is pushed U later.
- The yellow key at the beginning of Mr. McCallahan Presents requires a basic two-block nail to collect; there are two possible nails, either on [3, 7] or [2, 8], but only the former works in Lynx.