The element visible in the picture, called a nut, is a part of a ...
door lock
tap
bicycle hub
crossbow
Nut is a rolling cylindrical pawl. It 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.
reach: rather globalmechanicstechnologyweapons
Answers by country
door lock
tap
bicycle hub
crossbow
answers
the Netherlands14
Greece10
Poland11695
the United States71
the United Kingdom66
Germany51
Republic of Ireland22
India41