However, Colin, your description doesn't fit the operation of the Digi-Key part illustrated. The Digi-Key strain relief is such that you insert the cord into the strain relief, insert the "blade" into the slot and then (preferably using the special tool made for such things), squeeze it together and insert into a specially-shaped hole (round with two opposing flats) and release. Regular combination pliers can be used to insert the things, but you do bugger up the plastic. And they will work with a round hole, but will turn in the hole.
There are different sizes for different size line cords. I have bunches of them because I'm a scavenger and tend to save every part when scrapping out a piece of equipment.
Dean