A buyer messages and says the mailer arrived open. Or arrived empty. You know what you packed, tracking only says the package moved, and a mailer flap looks the same in a photo whether it was opened or not.
The package is the outermost layer of everything you ship, and it is the layer nobody photographs. A numbered Serial Seal™ across the flap gives you something to photograph and a number to log against the order — you pick the prefix and where the sequence starts on the builder, and it counts up from there. Here is where it goes on the two outers card sellers actually use, and what it is worth afterwards.
The sizes you are working with
Bubble mailers are sold by number, and outside size and usable inside size are both published and both different. A #000 is 4" x 8" outside with roughly 3.75" x 6.5" usable, and some brands list 4" x 7" instead. That is the hobby default for one card in a holder. A #00 is 5" x 10" outside, about 4.5" x 8.5" usable. The flap on a #000 runs roughly 1.5" deep with a factory self-seal strip under a peel liner, and the joint that matters is the free edge of that flap where it lands on the mailer body.
Boxes have no hobby standard. A 6" x 4" x 4" corrugated box is the common outer for a graded slab, 7" x 5" x 3" the other frequent pick. Both are regular slotted cartons, so the joint is the centre line on the top face.
Where the seal goes
On a mailer: one seal, on the back, laid vertically across the flap's free edge. The seal is 0.75" x 1.77". The flap lies flat on the body there, so centred on that edge it puts about 0.885" on the flap and 0.885" on the mailer body — a little over half the depth of a 1.5" flap. Across the width it covers 0.75 / 4 = 18.75% of a #000, or 15% of a #00. A single is right here: the flap edge is where the closure opens, and a fold wants a clean edge rather than a step.
You can fold one over the mailer's closed top edge instead if you prefer the wrapped look. Per-face landing is (1.77 - T) / 2, where T is the thickness of the edge being wrapped. A #000 loaded with a top loader closes at roughly 0.4" thick, so (1.77 - 0.4) / 2 gives 0.685" per face. In our own handling, folds stop holding once the landing drops to roughly 0.55 to 0.58 inches per face — that is an impression from sticking them down on our own bench, not a spec, so wrap one over your loaded mailer and pull at it.
On a box: one seal across the centre flap seam on the top face. The two flaps are level with each other, so it lands about 0.885" on each half, and that covers very little of the seam. On a 6" x 4" x 4" box the seam runs the full 6", so a seal in the middle sits on 12.5% of it. Two at the quarter points cover it far better.
| Package | Outside size | Style | Landing |
|---|---|---|---|
| #000 mailer, flap edge | 4" x 8" | Single | ~0.885" flap / ~0.885" body, 18.75% of the width |
| #00 mailer, flap edge | 5" x 10" | Single | ~0.885" each side, 15% of the width |
| #000 mailer, closed top edge, ~0.4" loaded | 4" x 8" | Fold |
(1.77 - 0.4) / 2 = 0.685" per face |
| 6 x 4 x 4 box, top seam | 6" x 4" x 4" | Single, use two | ~0.885" per flap half, 12.5% of the 6" seam each |
| 7 x 5 x 3 box, top seam | 7" x 5" x 3" | Single, use two | ~0.885" per flap half, 10.7% of the 7" seam each |
Kraft or poly
Kraft-faced mailers and corrugated boxes are fibre, so a seal pulled off one takes some of the outer liner with it. Poly-faced mailers are slick film, and most adhesives release from film cleanly. Pick your outer on cost and fit.
The choice changes what the seal peels off, not what the seal is: the same holographic vinyl at the same 0.75" x 1.77" either way. It is why the builder asks you for a prefix and a start number and never asks which mailer you buy.
Step by step
- Pack the item in its own holder first and seal the holder — not the card, not the penny sleeve. See the top loader guide. For a break bundle, band and seal the stack before it goes in, per the break stack guide.
- Close the mailer with its factory strip, or tape the box seam as normal, and press that closure down along its full length. The seal is not a substitute for it.
- Apply the seal to the back of the mailer, vertical, centred on the flap's free edge, serial reading right way up. On a box, two across the top seam at the quarter points.
- Burnish for 20 to 30 seconds with a thumb or the flat edge of a card. A half-stuck seal lifts in transit and the serial arrives scuffed.
- Photograph it: one tight shot where the serial is legible, one wider shot with the package and the address label in the same frame.
- Log the serial against the order number wherever you already work. A photo with no logged number is half a record. Keep both until the return window closes.
What this does and does not do
The seal sits on the outside of the package. It is the most reachable piece of adhesive film on the shipment, and someone can peel it off and put a different one in its place. Fold or single, kraft or poly, none of that changes, and we will not pretend otherwise.
What you have instead is the number. We printed the run in sequence, and you wrote down which serial went out with which order before the package left your bench. The seal is how that number rides where a camera can see it. Tape and a blank sticker close the flap the same way and leave you nothing to check a photo against later.
eBay, Whatnot, TCGplayer and the payment processors each run their own cases on their own rules, and those rules change. A logged seal makes what you hand over specific instead of general: this package, this date, this serial. Whether specific counts for anything in a given case is their call, and we have no way to know.
How many do you need
Count parcels, not cards. A mailer takes one seal. A box takes two, because a 6" or 7" flap seam is too long for one in the middle. Price it off one ordinary month rather than a formula. Take a month of 40 mailers and 10 boxes: 40 seals for the mailers, 20 for the boxes, and five per hundred more for the ones you set down crooked, so 63. Longer answers are that month multiplied — a quarter is 189, a year is 756.
At 189 you sit past the 120 rung at 45c a seal, so 192 — sixteen packs — is $86.40. The 600 rung, at $240.00 (40c each), costs not quite three times as much and lasts more than three times as long. At 756 you are past 600, so the whole run prices at 40c — $302.40 — and the rate keeps stepping down for bigger runs, through 36c at 1,200 and 33c at 2,400 to 30c at 4,200, where it finally holds.
Ship five mailers a week and the arithmetic is shorter. That is about 22 a month: the 60-seal minimum at $30.00 (50c list) is not quite three months of shipping, and 120 at $54.00 (45c each) carries you most of half a year.
60 Serial Seal™ minimum · From $30.00 · As low as $0.30 each in bulk. No setup, die, or design fees. Commercial license and copyright included.
Seals come in packs of twelve and sixty is the smallest order, so round your answer up to the next twelve. The rate applies on its own at checkout, one tier per order, and runs past 10,008 are quoted individually — ask us. Quantity is one field on the builder; change it and the price follows.
Common mistakes
- Putting the seal where the carrier label goes. A seal under a label is invisible, and one on top of a label can interfere with the scan. Use a face the label will not touch.
- Placing it at an outer edge or a corner. Automated sorters catch lifted edges. Keep it half an inch in from any outside edge, flat and burnished.
- One seal on a 6" or 7" box seam. The seam is long and the flaps flex. Use two.
-
Folding over a loaded mailer without testing it. Run
(1.77 - T) / 2for your own thickness, wrap one, and pull at it. - Sealing the package and never logging the number. The number is the product. Unwritten, it is a decoration.
Questions people ask
Should the seal go on the package or on the item inside?
Both, if you want. The package seal carries the order-level number and gives you the closed-and-shipped photo. The item seal goes on the holder — top loader, one-touch, bag — never on the card itself and never on a penny sleeve. Factory-sealed wax is its own case, and the answer there is mostly don't: see the sealed wax post.
Can I put a seal on top of the shipping label?
No — it can interfere with the carrier scan. Back of the mailer across the flap edge, or the box's top seam clear of the label.
A buyer says the package arrived empty. What does the seal give me?
A dated photograph of that package closed, with a serial in frame that matches the number logged against their order. That is a record you can send. What the marketplace does with it is theirs to decide.
What you buy is a run of holographic vinyl seals, numbered in sequence, one per parcel. Sixty is the minimum order — $30.00, 50c a seal — and the rate falls to 40c at 600 and keeps falling to 30c at 4,200, which is the floor for anything larger. Pick a gallery design and set your numbering on the builder, or put your own logo on them from the add a logo page. What makes a number on the outside of a parcel worth anything later happens at your bench: the serial goes on the package, and the same serial goes next to the order before it ships. The return-fraud page walks through what that log looks like when a buyer disputes what turned up.
Serial Seal is an independent printer. We are not affiliated with, endorsed by or sponsored by PSA, Beckett, CGC, SGC, Ultra Pro, BCW, eBay, Whatnot, TCGplayer or any card manufacturer. Brand names are used only to describe the products they make. Nothing here is legal advice.