Measure before you open the range
Pick from the six sizes. If none is close, use single wall rather than a crash lock that is mostly air.
A crash lock box opens into shape and has a peel-and-seal strip. The page for Crash lock boxes is where Packaging Boxes shows that line.
The published limit, if there is one
The category describes the board as 150K/T, recyclable and biodegradable, and sized towards Royal Mail small parcel guidelines. It lists six sizes.
A tape-closed cube is the right box when the size you need is not one of those six, or when the goods are not a small parcel.
Write the size down
Reorder the size from the six, not a made-up dimension.
At Packaging Boxes, Crash lock boxes does not change the cutoff. Orders by 3pm leave the same day. Under £50 ex VAT the delivery is still available. It is just not the free threshold.
Open Crash lock boxes when you already know this line. Pack quantities differ by size. Read the one you are buying. Packaging Boxes will still dispatch an order placed by 3pm on the same day.