Bag hardware is strap geometry, not jewellery. A side-release buckle, a D-ring, a lobster clasp and a ladderlock each fail in a different way: the buckle pops, the ring ovalises, the gate opens, the webbing slips. Spec the part by function and webbing width, then pick the metal or the polymer.
Closures and gates
Side-release buckle (插扣) is two pieces, male into female, opened by squeezing the barbs. Apparel and bag mills run them in PA66 nylon or PP. Look at barb spring-back and whether the webbing slot is single (fixed) or double (adjustable). This is the backpack chest strap and many belt-bag closures.
Lobster clasp (spring hook, 龙虾扣) is a gated snap hook. Fashion bags use zinc for looks; outdoor and marine use 304 / 316 stainless. Swivel versions stop the strap from twisting. Heavy industrial spring hooks (DIN 5299 territory) are lifting gear — do not put them on a fashion brief and expect a jewellery plate.
Related gates: dog-leash style hooks (heavier), carabiner-style gates with a lock (not a bag default), stamped sheet-spring clips (301 stainless in mill talk).
Rings and adjusters
A D-ring is a load spreader at a strap join. A ladderlock / triglide (日字扣) is a three-bar slider that shortens webbing; a two-bar “日” versus three-bar “目” distinction in Chinese mill language is about how the webbing is laced, not about jewellery. Edges must be broken so they do not cut the tape.
Plastic sliders (PP, POM, nylon) are light. Zinc and stainless take real load. Trade tables that assign kilograms to each polymer are order-of-magnitude only — test on the webbing you will ship.
Cord locks, J-hooks on removable straps, and metal “O” rings are the rest of the usual backpack kit.
Metals and tests
Zinc for plated fashion. Steel, zinc-plated, for dry indoor cheap. Stainless for wet. Aluminium for climbing-adjacent weight (and crush risk). Plating still wants salt-spray talk and REACH nickel on skin-contact fashion hardware.
Spring wire, when it is a real spring, is a steel spec (Chinese spring-wire GBs exist). For apparel bags, the buyer test that matters is open-close cycles, gate return, and strap pull on the sewn assembly.
Common webbing widths are 20, 25 and 38 mm; a 32 mm lobster on 25 mm tape is a mismatch, not a design. Plastic ladderlocks in regenerated resin can lose a large share of strength versus virgin PP or POM — ask for virgin if the strap is load-bearing. Metal sliders want a plate thick enough for salt spray; mill talk often starts around several micrometres of nickel, then a real cabinet test.
Fashion zinc lobster clasps are jewellery until a camera bag is dropped. Outdoor 316 gates are marine until someone specifies a gold plate that hides pits. Write the use: keyring, shoulder strap, haul loop. Then write the metal.
TrimGem quotes bag hardware as width + function + substrate. “Gold buckle” is not a line item.