I want to sew some facemasks. One I bought off ebay a while back has these handy plastic bits on the ear elastic to tighten and adjust the mask. Wanted to replicate but can't find these bits to buy as I've no idea what they would be called to search on internet. Found cord locks but they are all too big comfort wise. These bits are small and soft plastic and just slide up and down. Thumbnail in pics for size reference. Any ideas what to search for? Are they even a purchasable thing?