Lever 1 turns about axis A of upper shoe a. Flat spring 2 tends to hold lever 1 in the vertical position. In the working stroke, lever 1, together with the whole upper die, descends, passing through the next hole punched in strip b. The lower end of lever 1 runs against a bevel on lower die c and slides along this bevel, thereby advancing strip b the required amount.
$420$SL,SF$