These are my personal favorite embroidery hoops.
Plastic hoop with a tongue and groove system that keeps your work tight in the hoop. Easy to tighten and loosen with a metal screw.
Available in 4", 6", 8" or 10"
Book: The Mending Directory by Erin Eggenburg
Beeswax for Mending
Wooden Darning Loom by Katrinkles
Leather Hexagon Palm Thimble with Inserted Metal Adjustable Palm Thimble