Lancet assemblies for puncturing the skin and creating an incision. Upon activation, the disclosed assemblies are configured to move through a firing sequence in which a puncturing instrument extends through an aperture in the device and then is retracted back into a housing of the device and cannot be re-fired. The assemblies are designed so that the aperture in contact with the incision site does not move relative to the incision site during the firing sequence. Accordingly, the tolerance of the assembly is reduced and the reliability of the incisions created by the assembly, including the depth and width of such incisions, is increased.
