These are stainless bails made for knives with the lanyard hole. We have also used them on sheaths with rivets, etc. There are two sizes. The small is the same size that comes on GEC knives and will fit most knives. The large is big enough for thicker knives, such as a fixed blade or the GEC #35 Calf Pen.
You will need to spread and close these evenly from center to make sure consistent shaping when installed. Pliers with covered teeth to prevent marking are what we use to install. It does take a little patience to do correctly.