It is used to apply glue. It has the advantage of being slightly heavy so that it is easy to hold steady in the hand and the metal makes it easy to remove glue. Of the three, I often use the W-164mm spatula shown in the figure below. An alternative tool is a toothpick. Please refer to the website link for detailed features and prices.
Website：Unknown brand page, Google shopping
SIze：W-173, 175, 164 mm