The Dürkopp 18 is a quite unique patcher machine because it has a very narrow tip and can sew in very tight spaces other patchers probably would not be able to reach. It also has not an oscillating / elastic hook like all other patchers. Instead it has a "boat shuttle" in a fixed position and a "thread hook" which grips the upper thread pulls it back and thread slides around the shuttle and is forming the knot with the bottom thread (basically). This Video shows is quite good (not my video):