BALANCE SPRING STUD FOR A TIMEPIECE

Balance spring stud including, around a housing receiving a balance spring of reference thickness, a one-piece component made of a shape memory alloy and including two lugs, each arranged to rest on one of the surfaces of the balance spring, and wherein, in the free state, the minimum width of the air gap of the lugs is greater than the maximum value of the reference thickness when the component is in an open position corresponding to a martensitic structure, and wherein the maximum width of the air gap is less than the minimum value of the reference thickness when the component is in a closed position corresponding to an austenitic structure, and the balance spring includes an area of lesser thickness having a minimum thickness equal to the reference thickness, surrounded by areas of large thickness having a minimum thickness greater than the reference thickness.