Side Loading Tab Lock Mailers for Flat Goods
A side loading tab lock mailer is a slim corrugated wrap that you fill from one end, then close with a flap and two locking tabs. It suits art prints, books, calendars, records and anything flat that has to arrive without bent corners.
From £0.25 a box exact price on a written quote, within one working day
- Free design proof before anything is printed
- Production takes 4 to 6 working days after proof approval
- Free tracked UK mainland delivery in 2 to 3 working days
- Misprints or damage reported within 10 days with photos are reprinted or refunded
- Low minimums, quoted per job
Specification
What side loading tab lock mailers from us are made of and how they are measured. Anything not listed here, ask in the quote.
| Style | Slim end-loading wrap closed by a flap and two push-in tabs |
|---|---|
| Board | Brown kraft or white-lined, E-flute 1.5 mm or B-flute 3 mm |
| Size range | 100 x 80 x 30 mm to 600 x 450 x 450 mm, inside |
| Typical start | 300 x 220 x 50 mm inside, adjusted to the item |
| Plain, one colour, two colours or full colour, outer face or both faces | |
| Finish | Matt or gloss varnish, white underprint available on kraft |
| Inserts | Board stiffeners, dividers and paper void fill, quoted with the mailer |
| Supplied | Flat, creased and bundled for quick packing |
| Price | From £0.25 a box; exact price depends on size, board, print and quantity |
How to measure for a side loading tab lock mailer
Measure the item, or the stack, along its long edge, across its width and through its thickness. Add 3 to 5 mm to the length and width, and 2 to 3 mm to the thickness for a snug slide.
Send the three figures as the inside size. For a slim mailer, tell us if you want to stay inside a postal band, because a few millimetres of board can decide which band it falls in.
Which board for which job
E-flute at 1.5 mm keeps a side loader slim and crisp, and it is the usual choice for prints and books. B-flute at 3 mm adds stiffer walls for large posters on board, framed pieces or stacks that would flex in a thinner wrap.
Design Your Side Loading Tab Lock Mailer Box
Drop your logo on a real photo of our side loading tab lock mailers, set the size and quantity, and send it. A designer sets up the real dieline and sends a free proof.
Your logo is placed on a real photo of our box. A designer redraws it to scale on the dieline and sends a free proof before anything is printed.
What is a side loading tab lock mailer?
It is a flat, wide box made from one die-cut sheet. Unlike a mailer with a hinged lid, it stays closed along both long edges and the top. You open one short end, slide the contents in, then fold the end shut.
The end closure has a main flap and two small tabs. The tabs push into slits in the side folds and lock the flap down. It belongs with the other designs in our mailer box styles range, as the flattest of the group.
How does the tab lock close?
Packing a side loader is quick once the blank is folded, because you never lift a lid or fold walls around the item.
- Fold the blank along its long creases so it forms a flat sleeve with one end already closed.
- Slide the print, book or stack in through the open end until it meets the far wall.
- Fold the two small side flaps in over the end of the item.
- Bring the main end flap down and push both tabs into their slits until they sit flush.
- Press along the edges so the mailer lies flat, then add the address label to the top face.
The tabs grip without tape. A sticker across the end flap is a tidy extra if the parcel will be handled a lot on its way.
What can you post in a side loading mailer?
Anything thin and rigid enough to slide, where bent corners would spoil it.
- Art prints and photographs backed with a sheet of card.
- Hardback and paperback books, one or a short stack.
- Wall calendars, planners and diaries.
- Vinyl records and framed pieces with shallow frames.
- Notepads, greeting card packs and sticker sheets.
- Brochures and catalogues for trade customers.
If most of your parcels are paper, also look at literature mailers for printed matter, which open from the top instead.
What size side loading mailer do I need?
Width and length need clearance so the item slides in, but the thickness should be close. Too much depth lets a print slap about and catch its corners.
| Item | Inside size to start from | Band to check |
|---|---|---|
| A4 print on backing card | 305 x 220 x 10 mm | Large Letter |
| A3 print on backing card | 430 x 305 x 10 mm | Small Parcel |
| Paperback novel | 200 x 135 x 30 mm | Small Parcel |
| Two hardback books | 300 x 220 x 50 mm | Small Parcel |
| 12-inch vinyl record | 320 x 320 x 10 mm | Small Parcel |
| Wall calendar | 310 x 240 x 15 mm | Small Parcel |
Our step by step guide on how to measure a mailer box shows where to put the ruler for books with rounded spines.
Can a side loader go as a Large Letter?
Yes, when the outside stays within 353 x 250 x 25 mm. An A4 print backed with card fits comfortably in E-flute, which adds only about 3 mm to the depth.
A3 prints and records are too wide for that band and go as a Small Parcel, which allows 450 x 350 x 160 mm. Check the current band limits before you order. The Royal Mail band size guide explains how outside size is measured.
E-flute or B-flute for a side loader?
Most side loaders are made in E-flute. At 1.5 mm it keeps the mailer thin enough for letter bands, and it folds into tight, square edges that protect print corners.
B-flute at 3 mm suits wide mailers over about 350 mm, records, or anything with a glass front. The thicker wall resists bending when a postal worker carries it one-handed. We set out the trade-off in our comparison of E-flute and B-flute.
Printing a side loading tab lock mailer
The large top face gives a clean, even surface for a logo or a full pattern. One colour on kraft looks crafted and calm. White-lined board, with a white outside and a brown inside, gives full colour a bright ground, as seen on our white mailer boxes made to size.
The inside can be printed too, though the customer sees less of it than in a lidded box. A short line on the end flap, where the tabs lock, is often enough. Matt or gloss varnish keeps print from scuffing as the mailer slides through sorting.
Stopping flat items sliding inside
A print that moves inside the mailer can crease against the end flap. Size the length and width with 3 to 5 mm of clearance and keep the depth tight.
For thin prints, add a board stiffener cut to the inside size, quoted with the mailer. For a book in a deeper wrap, a folded sheet of paper void fill at each end stops it shifting.
How side loaders arrive and store
Side loaders come flat and creased in strapped bundles, delivered free and tracked to the UK mainland in 2 to 3 working days. Because they are already so thin, a bundle of a few hundred sits on a single shelf.
Keep the bundles flat under light weight so they do not curl in a damp room or a warm loft. Fold each one only when you pack, and keep the strap on the rest so the stack stays square.
Mistakes to avoid with side loaders
- Adding generous depth so prints rattle and dent their corners.
- Measuring a book without its dust jacket.
- Printing fine text across the tab slits, which cut through it.
- Picking B-flute for an A4 print and missing the Large Letter band.
- Putting the address label on the end flap, which is opened first.
- Forgetting the backing card when measuring a print, so it will not slide in.
How to order side loading tab lock mailers
Send the inside size, the board, the print and a quantity. We reply in writing within one working day, from £0.25 a box. A free proof comes first, and nothing is printed until you approve it.
Production takes 4 to 6 working days after approval. Report any misprint or damage within 10 days with photos for a reprint or refund. Ask for a price for side loading mailers or call +44 7578 382054.
Related mailer boxes
Other closures and finishes that start from the same idea.
Literature MailersShallow and rigid for brochures, prints and samplesFrom £0.25 a box
End Open Mailer BoxesShort-end opening for books, frames and setsFrom £0.25 a box
White Mailer BoxesWhite-lined board, printed or left plainFrom £0.25 a box
Folding Small Mailing BoxesFlat-packed, folds up in seconds, from 100 mmFrom £0.25 a boxSide Loading Tab Lock Mailers questions
Does a side loading tab lock mailer need tape?
No. The two tabs push into slits and hold the end flap down. Tape or a sticker over the flap is optional.
Can a side loading mailer be opened at both ends?
We usually close one end permanently and leave one end to load. A tab lock at both ends can be cut on request and is shown on the proof.
Will an A4 print fit a side loading tab lock mailer as a Large Letter?
Yes, an A4 print on a backing card fits a mailer around 305 x 220 x 10 mm inside, which stays within the Large Letter limits in E-flute.
How thick can a side loading mailer be?
Side loaders work best up to about 80 mm deep. Beyond that a lidded style is easier to pack and gives better protection.
Can I post a vinyl record in a side loading tab lock mailer?
Yes. A square mailer around 320 x 320 x 10 mm takes a 12-inch record in its sleeve, and B-flute adds stiffness for the post.
Is a side loading mailer stiff enough to stop prints bending?
The folded board resists bending, and a board stiffener cut to size adds more. For large prints, B-flute gives the stiffest wall.
Can the side loading mailer be white outside and kraft inside?
Yes. White-lined board gives a white outer face with a brown inside, which is the look in our photos.
Do side loading mailers come flat?
Yes, flat and creased in strapped bundles. Each folds into a sleeve in a few seconds.
Can a side loader hold several books at once?
Yes, as long as the stack is measured as one block. Add 3 to 5 mm to length and width and keep the depth close.
Where should the address label go on a side loading mailer?
On the large top face, away from the end flap. The flap is opened first and a label across it would tear.
Can the tab lock flap on a side loader be printed?
Yes. A short message or logo on the end flap is a common touch, kept clear of the tab slits.
Are side loading tab lock mailers quicker to pack than lidded boxes?
For flat goods they usually are, as you slide the item in and lock one flap. See how delivery works on our UK delivery details page.
Your question is not here? Ask on WhatsApp or call +44 7578 382054.
Tell us what you post
Send the product, a rough inside size and a quantity. We reply in writing within one working day with a price and a free design proof. Prefer to talk? Call +44 7578 382054 or message us on WhatsApp.