Pins are a new feature in Foldit, currently available in the devprev release.
A pin can hold a segment at a fixed point in space while other tools operate. Foldit has provided a video demonstrating the use of pins.
Each puzzle has at least one pin, initially located on the last segment, the N terminal.
Pins with a blue icon can be moved by dragging them to a new position on the protein. A pin can't be dragged across an open cutpoint, however.
Pins by default are "unlocked", and point perpendicularly to the backbone. Right-clicking (or shift-clicking) on a pin icon locks the pin, leaving it pointing toward the backbone.
Some puzzles, such as the Aflatoxin puzzles, have locked segments and permanent cutpoints. Puzzle of this type may have fixed pins, which have a gray icon, and which can't be moved or unlocked.
Pins do not affect the operation of the Move tool. A section of the protein, with a cutpoint or a N or C terminal on either end, can be moved freely with a locked pin in place. Pins also do not affect the Pull tool. When pulling on the backbone of the protein, the protein moves freely despite the presence of locked pins.
The underlying mechanism of pins has been present in Foldit for some time. The new pins reveals the pins, and lets the user adjust pins, moving them, and locking and unlocking them.
The feedback new Pins feature not as expected gives further background on how pins work.
There is no command to lock or unlock all pins. Pins can't be deleted. Closing a cutpoint removes a pin, and may move other pins. The initial pin (and any fixed pins) can't be moved.
There are no recipe functions for working with pins. Adding a cutpoint in a recipe adds a pin, but there is no way to control the pin's position or locked/unlocked status.