Crash lock boxes are cardboard boxes with a base that is glued and folded at the factory, so it drops into place and locks when you open the flat box out. The bottom needs no tape. You open the box, fill it and close the top, which is why a crashlock box is popular with online shops and subscription businesses that build boxes all day.
This guide explains how the crash lock base works and how to open one properly, then goes through the ten sizes we stock, CL-A to CL-K, with a note on what each one tends to hold. It also compares crash lock boxes with die cut boxes and standard taped boxes, says who gains from the faster base and who does not, and finishes with how to buy: minimum quantities, cost per box and delivery.
In This Guide
- Quick picks for fast-build postal boxes
- What is a crash lock box and how does the base work?
- How do you open and close a crash lock box?
- Which crash lock box size do you need, from CL-A to CL-K?
- Crash lock vs die cut vs a standard taped box: which should you choose?
- Who saves time with crash lock boxes, and who does not?
- Can you post a crash lock box, and what goes inside it?
- How many crash lock boxes should you buy, and what do they cost per box?
- Frequently Asked Questions
Quick picks for fast-build postal boxes
Three boxes cover most small and medium parcels, and which one suits you depends on depth, volume and how you like to pack.
Best for building boxes quickly
Crash Lock Boxes
Open the flat box and the base locks by itself, so the only tape goes on the top.
- 10 sizes, CL-A (100 x 100 x 70mm) to CL-K (426 x 300 x 300mm)
- Sold per box, minimum 5 per size
- Supplied flat, no tape on the base
From £0.59 ex VAT (£0.71 inc VAT)
Choose sizeView product
Best for one small product, no tape at all
Die Cut Boxes Brown 070502
A brown fold-together postal box that locks shut with its own folds.
- Pack of 50 boxes, supplied flat
- Folds together by hand without tape
- Plain brown card takes a label or sticker
From £20.00 ex VAT (£24.00 inc VAT)
Choose sizeView product
Best for flat items under 20mm
Royal Mail PIP Large Letter Boxes
Die cut boxes no deeper than 20mm, made for the Royal Mail Large Letter rate.
- Mini, C6, DL, C5 and C4 sizes
- Packs of 50, supplied flat
- Every size is 20mm deep
From £5.00 ex VAT (£6.00 inc VAT)
Choose sizeView productWhat is a crash lock box and how does the base work?
A crash lock box is a cardboard box whose base panels are glued together at the factory and folded flat, so that opening the box pulls the base down and locks it in place without tape. Some suppliers write it as one word, crashlock box, and others call it a crash lock bottom box or an automatic base box, but the box is the same.
An ordinary carton arrives as a flat tube with four loose flaps at each end, and you have to fold the bottom flaps in and run tape along the seam before anything can go inside. On a crash lock box the four base panels are cut at an angle and two of them are glued to their neighbours. When the box is flat, the base sits folded up inside the walls. When you square the box up, the walls pull those glued panels down and they meet in the middle, where they overlap and hold each other.
- What you get: a flat box that becomes a usable box in one push, with a base that needs no tape.
- What you still do: close the top flaps and seal them with tape or a label, whichever suits the way you post.
- What it is made from: cardboard, supplied flat. Our Crash Lock Boxes come in ten sizes and are sold per box, from £0.59 ex VAT (£0.71 inc VAT).
Our guide to slotted boxes and cardboard box styles covers the other box styles in detail, including the standard carton with flaps top and bottom.
How do you open and close a crash lock box?
You open a crash lock box by pushing the two opposite folded edges of the flat box towards each other until the box squares up and the base drops and locks. It takes one movement once you have done it a few times. The first box of a new batch can feel stiff, which is normal for board that has been stored flat.
- Find the base end. Hold the flat box and look at both ends. One end has loose flaps, which is the top. The other end has panels tucked inside the walls, which is the base.
- Hold it base down. Rest the base end on the bench, or hold the box in the air with the base pointing at the floor.
- Push the folded edges together. Put a hand on each of the two creased edges and press them towards each other. The flat box opens into a rectangle and the base panels swing down.
- Seat the base. Reach inside and press the floor down with your palm, or tap the box once on the bench. You should feel the panels settle flat. If the floor looks domed, it has not seated yet.
- Pack the box. Put the item in with any wrap or fill it needs. The weight of the contents helps keep the base locked.
- Close the top. Fold the top flaps in and seal them with tape, or with a label across the join if that fits the way you post.
For the top, one strip of tape along the centre seam is the usual close. Our Brown Packing Tape starts from £4.50 ex VAT (£5.40 inc VAT), and because the base takes none, a roll goes further on crash lock boxes than on cartons you tape at both ends. If you are unsure which tape to use, the packing tape guide goes through the types and widths.
Which crash lock box size do you need, from CL-A to CL-K?
We stock ten crash lock box sizes, coded CL-A to CL-K, running from 100 x 100 x 70mm up to 426 x 300 x 300mm. There is no CL-I in the range: the codes go from H straight to J. Dimensions are listed as length x width x height in millimetres. The inch figures in the table are our own conversions, rounded to one decimal place, so use the millimetres when the fit is tight.
| Code | Size in mm (L x W x H) | Approx. inches | What tends to fit |
|---|---|---|---|
| CL-A | 100 x 100 x 70 | 3.9 x 3.9 x 2.8" | Jewellery, small cosmetics, samples, a single small candle |
| CL-B | 160 x 150 x 75 | 6.3 x 5.9 x 3.0" | Small jars, skincare sets, a mug-sized item lying down, small parts |
| CL-C | 180 x 100 x 50 | 7.1 x 3.9 x 2.0" | Tubes, boxed accessories, long narrow items. The shallowest size at 50mm |
| CL-D | 220 x 111 x 78 | 8.7 x 4.4 x 3.1" | Bottles lying flat, glasses cases, small tools, boxed cables |
| CL-E | 252 x 136 x 88 | 9.9 x 5.4 x 3.5" | Small shoes or sandals, paperback bundles, toiletries sets |
| CL-F | 290 x 208 x 95 | 11.4 x 8.2 x 3.7" | An A5 item (148 x 210mm) flat with room to spare, folded clothing, subscription sets |
| CL-G | 320 x 200 x 130 | 12.6 x 7.9 x 5.1" | Shoes, small homeware, several products in one order |
| CL-H | 375 x 255 x 150 | 14.8 x 10.0 x 5.9" | A4 paperwork and brochures flat, boots, larger bundles |
| CL-J | 426 x 300 x 150 | 16.8 x 11.8 x 5.9" | An A4 item (210 x 297mm) flat with space around it, folded coats, multi-item orders |
| CL-K | 426 x 300 x 300 | 16.8 x 11.8 x 11.8" | The deepest size. Bulky homeware, stacked products, trade orders |
The "what tends to fit" column is only our judgement from the dimensions. Products vary and we cannot guarantee a fit, so check your item against the internal size before you order a quantity. If the fit comes down to a few millimetres, ring us on 0161 706 1246 and we will measure a box for you.
- CL-A is a small cube-ish box. At 100 x 100 x 70mm it suits one small product. Anything with a pump or a tall lid will need CL-B or CL-D.
- CL-C and CL-D are the long, narrow pair. CL-C is 180mm long and only 50mm high. CL-D is 220mm long with 78mm of height, so it takes the same kind of item with more wrap around it.
- A4 does not lie flat in CL-G. CL-G is 200mm wide and A4 is 210mm wide. For A4 items go to CL-H (375 x 255mm base) or CL-J (426 x 300mm base).
- CL-J and CL-K share a base. Both are 426 x 300mm. CL-J is 150mm high and CL-K is 300mm high, so you choose between them on depth alone.
To pick a size, measure the item at its longest, widest and tallest points, add the thickness of any wrap on every side, then choose the smallest box that clears all three measurements. A box that is much too big needs more fill and can cost more to post. Our guide to what size box you need walks through measuring in detail, and the small boxes guide compares the small sizes across all our box ranges.
All ten sizes on one page
Crash Lock Boxes
Pick a code from the size menu and the price per box updates as you change the quantity.
- CL-A to CL-K, 100 x 100 x 70mm to 426 x 300 x 300mm
- Priced per box, minimum 5 per size
- Price per box falls as the quantity rises
From £0.59 ex VAT (£0.71 inc VAT)
Choose sizeView productCrash lock vs die cut vs a standard taped box: which should you choose?
Choose a crash lock box when you build many boxes and want depth, a die cut box when you want a neat small mailer with no tape at all, and a standard taped box when you need the widest choice of sizes at the lowest price per box. All three arrive flat, and they differ in what you have to do before the product goes in and in how you close the box.
| Crash lock box | Die cut box | Standard taped box | |
|---|---|---|---|
| How the base forms | Pre-glued panels lock as you open the box | The whole box folds from one cut sheet, with tabs that tuck in | You fold four flaps and tape the seam |
| Tape needed | Top only | None to assemble. A strip or label on the lid is optional | Bottom and top |
| How it opens for the customer | Top flaps, like a carton | Hinged lid, like a shoe box | Top flaps |
| Our range | 10 sizes, CL-A to CL-K | Brown 070502, plus PIP boxes in 5 sizes at 20mm deep | Single wall in 15 sizes, 5 x 5 x 5" to 24 x 18 x 18" |
| How it is sold | Per box, minimum 5 per size | Packs of 50 | Per box, minimum 5 per size |
| Price from, ex VAT | £0.59 per box (£0.71 inc VAT) | £20.00 per pack of 50 (£24.00 inc VAT) | £0.35 per box (£0.42 inc VAT) |
Die cut boxes are cut from a single sheet and fold into a box with a hinged lid and tuck-in sides. Nothing is glued, and nothing needs tape to hold it together. They take a little longer to fold than a crash lock box takes to open, because there are more folds, but the finished box looks tidy and the customer lifts a lid to open it. Our Die Cut Boxes Brown 070502 come in packs of 50 from £20.00 ex VAT (£24.00 inc VAT). It is one model in one size, and we do not publish its internal dimensions on the listing, so call or email us to confirm them before you order.
Standard taped boxes are the ordinary carton. Our Single Wall Cardboard Boxes run from 5 x 5 x 5" (127 x 127 x 127mm) to 24 x 18 x 18" (610 x 457 x 457mm), from £0.35 ex VAT (£0.42 inc VAT) per box with a minimum of 5 per size. You tape the base yourself. In return you get more sizes, including cubes and large moving sizes that the crash lock range does not cover.
If your goods are heavy or fragile, the board the box is made from matters more than the style of base. Read corrugated cardboard explained for how single and double wall board differ, and look at our Double Wall Cardboard Boxes, from £0.59 ex VAT (£0.71 inc VAT), for heavier loads. For a closer look at the three mailer styles side by side, see letter box boxes: die cut, crash lock and PIP compared.
Who saves time with crash lock boxes, and who does not?
Crash lock boxes save the most time for anyone who builds boxes in batches: online shops with steady daily orders, subscription businesses packing the same box many times over, and retailers boxing products or samples. The saving comes from removing one job, taping the base, from every box you build. We will not put a number on it, because it depends on your bench, your tape gun and your hands. Time ten boxes of each type yourself and you will have a figure you can trust.
- Subscription packing days. You pack the same contents into the same size box for a few hours. Opening boxes one-handed while the other hand reaches for product keeps the line moving.
- Busy order peaks. When orders stack up before a sale or a holiday, the bench fills with half-built cartons. Crash lock boxes go from flat to open as you need each one, so nothing sits around waiting for tape.
- Shared or temporary packers. Someone helping for a day does not need to learn how to tape a base squarely. They push the box open and pack.
- Small benches. If you pack from a spare room, there is no space to pre-build twenty boxes. A stack of flat crash lock boxes takes little room, and each one opens when you reach for it.
- Retail and sample boxes. The base has no tape seam, so the box looks clean from underneath as well as on top.
In these situations we would point you somewhere else:
- A handful of parcels a week. Buy single wall boxes and tape the base. They cost less per box and come in more sizes.
- Flat items under 20mm. No crash lock size is that shallow. The shallowest, CL-C, is 50mm high. Use Royal Mail PIP Large Letter Boxes, which are all 20mm deep and come in packs of 50 from £5.00 ex VAT (£6.00 inc VAT).
- Clothes and soft goods that cannot be crushed. A mailing bag weighs less and costs less than any box. See the mailing bags collection.
- Heavy or fragile goods. Choose the board first. Double wall boxes are made for heavier and more fragile items.
- Printed or branded boxes. We sell plain stock boxes only and do not offer custom printed packaging. A plain box with your own sticker on the lid is the low-cost route, and our post on making stock mailer boxes your own covers it.
Can you post a crash lock box, and what goes inside it?
Yes, crash lock boxes are cardboard postal boxes: close the top, seal it, add your label and send it with Royal Mail or a courier. The base stays locked in transit because the contents sit on it and the glued panels cannot open outwards. Size and weight limits for each service change, so check the carrier for current limits before you settle on a box size for a product you sell often.
None of the ten sizes is a Large Letter box. The Royal Mail Large Letter thickness limit is 25mm and the shallowest crash lock box is 50mm, so every crash lock box goes as a parcel. If postage cost is the main concern and your item is thin, the large letter boxes guide explains what fits in a PIP box. The base is also a cardboard floor like any other, so anything that can break still needs wrapping.
What to put inside depends on the gap between the product and the walls:
- Snug fit, sturdy item: nothing extra. A boxed product in the right size crash lock box does not need fill.
- Breakable item: wrap it. Small Bubble Wrap starts from £9.00 ex VAT (£10.80 inc VAT).
- Loose item with space around it: fill the gap so the item cannot slide. The protective packaging collection has paper and air fill options.
For labels, check the top panel of the closed box against your label size before you buy a batch. A 4 x 6" label (101.6 x 152.4mm) is larger than the 100 x 100mm top of CL-A and wider than the 100mm top of CL-C, so on those two it will wrap over an edge. Our labels collection lists the sizes we stock.
How many crash lock boxes should you buy, and what do they cost per box?
Crash lock boxes are sold per box with a minimum of 5 per size, from £0.59 ex VAT (£0.71 inc VAT), and the price per box falls automatically as the quantity rises. Across the ten sizes, prices run from £0.59 to £4.50 ex VAT (£0.71 to £5.40 inc VAT) per box depending on size and quantity. The tiers for each size are shown on the product page, so you can see the saving before you add to basket.
A sensible way to buy is in three stages.
- Test with 5. Buy the minimum of the size you think is right, and of the next size up if you are unsure. Pack real orders.
- Buy a month's worth. Once the size is settled, work out how many of that product you send in a month and order that many. Look at the volume tiers on the page: if you are a few boxes short of the next tier, rounding up can lower the price of every box in the order.
- Move to a regular order. If you are reordering the same sizes every few weeks, open a trade account. For pallet quantities, call 0161 706 1246 and we will quote.
The starting prices give a rough comparison of cost per box across the styles. A pack of 50 die cut boxes at £20.00 ex VAT works out at 40p per box at the single pack price. A pack of 50 PIP large letter boxes from £5.00 ex VAT works out from 10p per box. Single wall boxes start from £0.35 ex VAT each and crash lock boxes from £0.59 ex VAT each. Those are starting prices for the smallest sizes, and the sizes are not the same across ranges, so use the product pages for the exact price of the box you need. Then add the tape you would use on a taped base and the time it takes you: at ten parcels a week the taped box is usually the cheaper buy, and the crash lock base pays for itself once you spend a good part of the day building boxes. Our guide to buying mailer boxes in bulk goes further into quantities.
Delivery works the same way for every box we sell:
- Free delivery: Royal Mail Tracked 48 is free on every order with no minimum.
- Same-day dispatch: orders placed by 2pm Monday to Friday leave our Manchester unit the same working day.
- Click and collect: free from Cheetham Hill, Manchester, usually ready within 2 hours.
- Local van delivery: same day within 10 miles of Cheetham Hill. See local delivery in Manchester.
- Invoices: a VAT invoice comes with every order.
Boxes arrive flat, so even a few hundred take up a shelf or the space under a bench. If you are not sure which size to start with, send us the dimensions of your product through the contact page and we will suggest one.
Frequently Asked Questions
What is a crash lock box?
A crash lock box is a cardboard box with a pre-glued base that folds down and locks into place when you open the flat box. The base needs no tape, so you only seal the top. A crash lock box is also called a crashlock box, a crash lock bottom box or an automatic base box.
Do crash lock boxes need tape?
Crash lock boxes do not need tape on the base, because the glued base panels lock together when the box is opened. You still close the top flaps of a crash lock box and seal them with tape or a label. One strip along the centre seam of the top is the usual method.
What sizes do crash lock boxes come in?
Pack Solution stocks ten crash lock box sizes, from CL-A (100 x 100 x 70mm) to CL-K (426 x 300 x 300mm). The sizes in between are CL-B (160 x 150 x 75mm), CL-C (180 x 100 x 50mm), CL-D (220 x 111 x 78mm), CL-E (252 x 136 x 88mm), CL-F (290 x 208 x 95mm), CL-G (320 x 200 x 130mm), CL-H (375 x 255 x 150mm) and CL-J (426 x 300 x 150mm). Dimensions are length x width x height.
Which crash lock box fits an A4 item?
The CL-J crash lock box (426 x 300 x 150mm) takes an A4 item (210 x 297mm) flat with space around it, and the CL-H (375 x 255 x 150mm) also has a base larger than A4. The CL-G is 200mm wide, which is narrower than A4, so an A4 item will not lie flat in a CL-G. Check your item against the internal size before ordering a quantity.
What is the difference between a crash lock box and a die cut box?
A crash lock box has a glued base that locks as you open the box, and top flaps that you seal with tape. A die cut box is folded from one cut sheet, has a hinged lid, and holds together with tuck-in tabs so it needs no tape to assemble. Crash lock boxes are quicker to open and come in deeper sizes, while die cut boxes suit small products and give a lift-the-lid opening.
Can I buy crash lock boxes in small quantities?
Yes. Pack Solution sells crash lock boxes per box with a minimum of 5 per size, from £0.59 ex VAT (£0.71 inc VAT). The price per crash lock box falls automatically as the quantity rises, and the tiers are shown on the product page. Royal Mail Tracked 48 delivery is free on every order with no minimum.
