Image Number 4 for United States Patent #4485709.
A sliding block with a female die acts in conjunction with a four bar linkage mounted block with a male die to punch indexing holes in a moving metal strip. The block with male die continually seeks to rotate, but is held in position by the sliding block. The sliding block is programmed to periodically move forward at the speed of the moving metal strip and to return to starting position. This frees the male die to rotate to punch out the hole, and to continue to rotate back into the starting position to be held by the returned sliding block.