Should an ordnance packing box cavity include clearance?

Answer: Yes, 5 mm a side for gloved handling. Die-cut foam allows 3 mm, but keep 10 mm on top.

Can the wall be 4 mm instead of 5 mm?

Answer: Not in rotomoulding: at 4 mm it thins to 3.4 mm locally and bulges after two years of stacking. Ribbed injection parts can reach 3 mm.

The sheet says 200 kg, so can I load 200 kg?

Answer: No. That is a distributed floor load with nothing left for stacking; work back from gross weight and stack count at 1.5.

Is ±2 mm on the cavity tight enough?

Answer: Under 800 mm, yes. Above that, shrinkage makes ±3 mm realistic; forcing ±2 mm only raises the reject rate.

Does the sheet need a sealing class?

Answer: Yes, IP67 plus the factory pressure figure. "Waterproof" alone gives both sides nothing to test against.

Ordnance Packing Box Specifications: Size, Wall and Load

Quick answer: An ordnance packing box is specified from the cavity outwards: payload envelope plus 5 mm a side, an outside that closes the wall-and-rib chain, walls from 5 mm with 8 mm corners, and load checked as stack weight times 1.5.

How an Ordnance Packing Box Specification Is Built
Wall Thickness by Moulding Process
Load Stacking and Safety Factor
Tolerances and Sealing Class
Four Lines the Sheet Usually Misses
FAQ

1. How an Ordnance Packing Box Specification Is Built

A specification sheet usually starts at the outside. The cavity is the origin: measure the payload envelope, add 5 mm a side for gloved handling, then add wall and rib back.

Item	Value	Basis
Cavity	780×480×360 mm	Payload plus 5 mm a side
Wall and rib	5 + 8 mm	Minimum section, load path
Outside	806×506×386 mm	Cavity plus 2×(wall + rib)

The chain has to close: taking the wall from 5 to 6 mm grows the outside 2 mm per face and breaks a two-across pallet pattern. Keep 10 mm between the payload top and the lid liner, or the foam compresses hard and the clamp load lands on the latches.

2. Wall Thickness by Moulding Process

Wall thickness is the first item squeezed because it maps onto weight and price. The cost of thinning does not appear in the new box; it appears two years later, in the stack.

Ordnance packing box: two workers in khaki coveralls lift an olive case onto a pallet, an open case showing black foam cavities on the bench

Rotomoulding runs 5–6 mm with 8 mm corners and 13.5 kg; injection runs 3–4 mm with ribs and 6.8 kg under 60 L; blow moulding runs 6–8 mm at 11 kg for long shapes. Rotomoulded wall follows powder charge and dwell, so one box varies 0.6 mm: write "5 mm, nowhere below 4.5 mm", not 5±0.1. Injection ribs run 0.6 times the wall, thicker and the outer face sinks.

3. Load Stacking and Safety Factor

Load is three numbers, not one: static floor load, stack load and transport impact. At 45 kg gross and four high the bottom box carries 135 kg; a 1.5 factor gives 202 kg with 1.5 mm of base deflection over 24 hours at 25 °C, nearly double that at 50 °C.

Stack	Bottom load	Checked value	Deflection
3 high	90 kg	135 kg	≤1.2 mm
4 high	135 kg	202 kg	≤1.5 mm
5 high	180 kg	270 kg	≤2 mm with board

Transport is two lines: a 0.8 m six-face drop at full load with no crack and no latch release, then two hours of random vibration from 5 to 200 Hz with fasteners tight.

4. Tolerances and Sealing Class

Tolerances decide whether two batches can be swapped, so they are measured after 24 hours of cooling; shrinkage of 2%–3% pulls large mouldings off size.

Ordnance packing box: three olive cases stacked on a steel rack beam, two latches and a metal handle each, an open case with egg-crate foam

Item	Tolerance	Check
Cavity under 800 mm	±2 mm	Tape and gauge
Cavity over 800 mm	±3 mm	Tape and gauge
Wall	±0.4 mm	Ultrasonic gauge
Hole centres	±0.3 mm	CMM

IP67 covers the sealing class, plus one line for the factory test at 20 kPa held 60 seconds: 1 m of water for 30 minutes, short immersion rather than flooding.

5. Four Lines the Sheet Usually Misses

A sheet can carry size, wall and load for a page and still omit four lines that decide whether acceptance passes.

Service temperature, -40 to 71 °C: rotomoulded polyethylene softens from 71 °C, and a closed trailer passes 65 °C.
Hardware coating, 240 h neutral salt spray with no red rust.
Stack mark, short side, 300 mm up, or the crew guesses the layers.
Regrind ratio, 20% at most and never in load ribs, since 20% costs about 15% of impact strength.

Each is cheap to write and costly to argue about, so they belong beside the dimensions on the ordnance packing box drawing.

Conclusion

An ordnance packing box specification is calculated: the cavity comes from the payload envelope plus 5 mm, the outside closes the chain, walls follow the process floor, load is stack weight times 1.5, and tolerances and sealing need a test method. What holds the design up at drawing stage is that closed chain from cavity to outside on the ordnance packing box.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.