Draft
The nut stays on its square. Drag the shaft through it and let go. Availables, when turned on, outlines a bolt that can leave.
Drag the shaft through the nut and let go to park it. A bend cannot pass the nut, so a centered nut cannot leave left or right. Turn on Availables to outline a bolt that can leave.
Save this board writes the puzzle into the open catalog. Generate makes a Draft. Rename in the list. Drag ≡ to reorder that catalog.
The nut is fixed. The shaft slides through it along the nut's axis, and a bend stops against it. A bolt cannot cross the edge of the board. It comes off when the nut lets go while the shaft is still inside.
Open min / max is how many bolts can already leave. Leave max is the most that may be able to leave at once while the board is solved. Setups is how many times that number hits 0 and a slide that does not remove a bolt opens the next one. Min length skips shorter bolts. Blocks is how many other exits a new bolt should stand in.
Edit draws on the level that is open. Bolt extends from the end you click. Nut adds a collar on a straight cell, not a bend. Bolt erase removes the bolt. Nut erase removes only the collar. Each save adds a new level.
Generate and Validation use this. The Gridless button on the board only changes play.