Will this work for a 1 1/4 inch or 3/4 inch belt?
Yes, elastic strap/belt keepers fit 0.75" - 1.25" wide strap/belt, but it also depends on the thickness of belt or strap.
Are these velcro or is the loop sewn shut? How can I get it on dangling backpack straps?
Sewn. You need to either stretch it over the buckle or remove the buckle.
It's a loop that slides over a belt or other strap/webbing to hold down the loose end.
If you need this 1" elastic straps keepers in other colors, please contact us via Amazon for customization.
1.5" and 1.75"/2" elastic belt/strap keepers are also available in our store.