The swap that looks close
double wall is the usual substitute for single wall cartons on a repeat line, and it is the wrong one. Moving a heavy line onto a bigger single wall carton does not make it a double wall carton.
Packaging Wholesale lists Single wall boxes separately because the jobs diverge as soon as the goods are on the bench.
What the right line actually does
Single wall is the everyday board for a carton line you reorder by size.
The category describes single wall as strong, affordable and versatile. Double wall is the stronger board, manufactured in the UK, for heavy or fragile goods.
If you have already mixed them
Letting a near size substitute for a week trains the bench to pack badly.
At Packaging Wholesale, Single wall 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 Single wall boxes when you already know this line. Cartons are pack quantities. The page says how many are in the bundle. Packaging Wholesale will still dispatch an order placed by 3pm on the same day.