It is made from half inch cycle chain, 11 pitches long. The yoke piece is 5mm mild steel, the anchor holes are 9mm apart, and 11mm radius from the centre of the 3/8 square. It needs to be able to split to get it on and off. The loose pin is a length of nail.
Used with a long extension, it is a slight fiddle to get into place, and you need to get it to "catch", but beats removing the rack any day. Ensure the nail is on the trailing (lower tension) side.
Fred