The Famous Roller Nut
Most European medieval crossbow ‘s featured a roller nut release mechanism with a simple, single axle trigger (tickler). The nut was mostly made of horn.
Horn nuts are robust, and fast. They last a very longtime and where probably in most medieval crossbow ‘s.
Due to their flexibility, they sometimes crack the back of the nut socket when fired.
Sockets for horn nuts where fitted with a reinforcement of horn or metal behind the nut to prevent this problem. Many medieval bows reinforced the socket at front and back with blocks of horn.
Brass or bronze nuts are pretty and strong, though heavy and slow to release.
These nuts can cause a misfire due to their slow spin, and they waste a small amount of power due to their high mass. They do perform continually and need very little maintenance. Given the excellent alternatives available.
Steel nuts are faster than brass, though slower than horn. They last forever and are superb for very heavy draw bows (above 150 lb.). With very strong bows, they should be used with a reinforced socket.
The socket should take all the pressure of the nut when the bow string is stretched over the fingers of the latter, and for this reason the pin is slightly smaller than the hole in the center of the nut. If any strain came upon the pin, which passes through the nut, it would bend and the nut would not then revolve.
In many mediaeval crossbows, the pin through the nut was omitted, though sometimes present in the form of a thin length of string passed several times through the hole in the nut, and then round the stock, just to prevent the nut from falling out of its socket and being lost,
The nut always had its notch protected by a small wedge of hardened steel, which met the point of the trigger inside the stock.
Plastic, especially Derlin or Hydex are nowadays substitution. Delrin in particular is strong and self-lubricating. All my crossbows, up to 140 lb. are built with a Delrin roller nut.
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