This looks like a single crease that has been split into a double crease. A screw adjusts the distance between the two heads to give a line a chosen distance from the edge of a piece of work or as an adjustable double crease.
This looks like a single crease that has been split into a double crease. A screw adjusts the distance between the two heads to give a line a chosen distance from the edge of a piece of work or as an adjustable double crease.