Clear plastic butterfly hooks as seen on a custom point-of-purchase display. But this same style of hook that occupies but one-column-width of holes rather than the standard two-in-width are available for regular pegboard too. Their normal purpose is to allow high-density, shoulder-to-shoulder display of narrow product (Tooth brushes? Bolo ties? String bikinis? Travel size packs of Pipe Cleaners?). Here they may be in use as a design as well a cost-saving strategy … though make sure you bid the job both ways. I suggest that two-column-width plastic hooks are manufactured in far greater quantity and at lower cost than less-common, one-column-width hooks which use marginally less material. If you know which is cheaper in quantity, please post the answer as a comment.
Also compare label holder size and use at…
“Label Size vs Display Density”
“Rulers Sold On Hooks”
“Short Sheeted 3/4″ Deep Label Holders“
“Buy-One Get-One Flip-Front Selling Tool“
“How to Make a Flip Front Sign Holder”
“Narrow vs. Wide Label Holders.”