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A returnable crate is chosen by three numbers, and only one of them is about the part. The outside dimension has to sit on the pallet and pass the conveyor without overhang. The inside dimension has to hold the component with the dunnage around it. And the nesting ratio decides what the empty leg costs: this crate stacks to 35 kg working load and nests roughly three and a half to one when empty, so a truck that carried 120 crates out brings 420 back on the same deck.
The 600 x 400 mm footprint
This is the HP size most Japanese automotive lines were laid out around, which is why it slots into existing racking, roller conveyors and tugger trains without a layout change. Body shop stampings, sub-assembly kits and line-side buffer stock can share one pool instead of three container types, and a crate that fails inspection is swapped rather than redesigned.
Load path through the ribs
Ribbed walls carry the stack, not the base. Five crates at 35 kg puts 175 kg on the bottom unit, and the load travels down the corner posts and the wall ribs into the feet; a flat panel of the same weight would bow in the middle and jam the part on the way out. We quote the stack height with the crate, because a sixth layer is a different wall rather than a bigger number on the same drawing.
Handling, washing and colour
The hand cut-outs are sized so a gloved operator lifts a full crate without a hoist, and the smooth interior wipes down with the same detergent used on the line. Blue is the automotive loop colour; the same crate in red or grey marks a different part family, and the coloured masterbatch runs through the wall rather than sitting on it as a coating.
Dividers, lids and identification
Dunnage is cut to the part drawing: EPP inserts for cosmetic faces, PP dividers for mixed kits, and a lid where the top layer is exposed on the truck. Label pockets and barcode plates are moulded in, not stuck on, because an adhesive label that survives a wash line is a rare thing. Tooling is built in Zhangjiagang and a first sample is measured against the drawing before mass production starts.
If the return leg is longer than the outbound leg, the nesting ratio matters more than the crate price, and we will say so before quoting.
