Editing Crossbow (section)

=== European rolling nut lock ===

The earliest European designs featured a transverse slot in the top surface of the frame, down into which the string was placed. To shoot this design, a vertical rod is thrust up through a hole in the bottom of the notch, forcing the string out. 

This rod is usually attached perpendicular to a rear-facing lever called a ''tickler''. A later design implemented a rolling cylindrical pawl called a ''nut'' to retain the string. This nut has a perpendicular centre slot for the bolt, and an intersecting axial slot for the string, along with a lower face or slot against which the internal trigger sits. 

They often also have some form of strengthening internal ''sear'' or trigger face, usually of metal. These ''roller nuts'' were either free-floating in their close-fitting hole across the stock, tied in with a binding of sinew or other strong cording; or mounted on a metal axle or pins. 

Removable or integral plates of wood, ivory, or metal on the sides of the stock kept the nut in place laterally. Nuts were made of antler, bone, or metal. Bows could be kept taut and ready to shoot for some time with little physical straining, allowing crossbowmen to aim better without fatiguing.