What size shackle do I need for luggage zippers?

For zipper-pull locking on suitcases and backpacks, a small shackle in the 3–5 mm diameter range is typical. For hostel lockers you'll usually want a wider shackle (around 5–7 mm) and a body around 30–40 mm wide. Retailer listings for the Kawaha and SEDORTI picks below spell out shackle and body dimensions explicitly.