# A blank disc unlocks a trolley because the lock can't count > A shopping trolley's chain lock reads the size and weight of what's inserted, not what it's worth — which is why a plain metal disc with no face value works as well as a coin. August 22, 2026 · https://justog.club/stories/the-coin-you-keep-only-for-a-trolley One small disc, printed high on the left chest, the one mark on the whole shirt. No face value. No portrait. No writing stamped anywhere on it — just a milled edge and a ring worn into the centre where a thumb has rubbed it for years. It sits in a pocket for months at a time, doing nothing, waiting for one specific job. ## What is this, if there's no currency printed on it? A trolley token — a plain disc kept for the coin-operated chain lock some shopping trolleys still use, in case the coin it actually wants isn't in your pocket when you need one. The lock doesn't ask what the disc is worth. It asks whether the disc is the right size and weight to sit in the slot and release the chain. A token cut to that exact size does the job a coin does, without being a coin at all — which is the entire reason it's worth keeping one. ## Why does a blank disc work as well as an actual coin? Because the mechanism inside a trolley's chain lock is entirely mechanical — a slot, a chamber, a catch — and it has no way of reading value even if it wanted to. Drop something in that matches the slot's dimensions and the catch releases, whatever's printed on the face. A coin works because it happens to be the right size, not because the machine recognises it as money. Once you know that, a purpose-made disc stops being a substitute for a coin and starts being the object actually cut for that slot — sized for the lock, and nothing else about it needs to be true. ## Where does a token like this actually live, day to day? Somewhere it survives being forgotten about for weeks at a stretch — a key ring, a coin dish by the door, the same zip pocket every time — because the one moment it's needed is also the one moment you can't go looking for it. A token that lives loose in a bag gets lost between uses; a token clipped to keys that leave the house daily is there without anyone having to remember to bring it. The habit isn't really about the disc. It's about picking a spot for it once and not relitigating that decision every time. ## Whose permission do you need to print a plain metal disc? Nobody's — a blank disc with no face value, no portrait and no maker's mark isn't a design that belongs to anyone, so there's no licence standing between the object and the shirt. What would need clearing is an actual currency's design, or a specific retailer's branded token. This one carries neither — it's drawn as the generic, unbranded object the habit has been about the whole time. ## Isn't a coin-lock trolley a bit rare now that so many take a card tap or don't lock at all? Plenty have moved on, which is exactly why the token that still works everywhere is worth more than it looks — it's the version that doesn't care which system a particular car park has installed. [A rule that outlived the reason everyone gives for it](/stories/the-quarter-tank-rule) runs on a related logic — some habits keep paying off long after the specific justification for starting them gets murky, because the cost of keeping the habit is close to nothing and the cost of needing it once and not having it is a walk back to the car with an unlocked trolley waiting. ## Is this really that different from just keeping spare change around? Yes — spare change gets spent, and a coin sized right for a trolley lock might not be one you're willing to hand over at a till, whereas a token has exactly one job and doesn't compete with anything else for that role. [The button jar keeps every button a garment ever shed](/stories/the-button-jar), on the same principle — a small object set aside specifically because its one future use is worth more than whatever else it might otherwise be spent or thrown out for. ## Does it print well? Yes — a smooth disc with a milled edge and fine radial engraving is close to pure line work, which a screen print reproduces with almost nothing lost. One ink: silver on gunmetal grey, small and precise rather than bold — the whole point of the placement is that it reads like something worn rather than something announced. ## How do I get one made? Describe the token at [JustOG](/) — what it unlocks, how long you've carried it, and what's worn into it by now. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped. Designs other people have published are in the [shop](/shop). The pocket it lives in is empty of everything else today, and the disc is still there.