A knot tying tool can include an elongated housing and an insert member. The housing can have first and second body portions having different outer cross-sections. A first chamber can extend within the housing with a slit that opens into the chamber. The insert member can also have a slit opening into a second chamber. The insert member can have an inner cylinder rotatable and movable within the first chamber. Rotation of the inner cylinder within the first chamber can move the knot tying tool between a locked and an unlocked position, the first and second slits being aligned in the unlocked position to allow a line to pass through the first and second slits into the second chamber.