Blockmit DIY Washer Jig

Description

Blockmit DIY Washer Jig

Your seed phrase is the whole of your bitcoin, and it is probably sitting on a piece of paper. This is the cheapest honest fix: stamp your words into steel washers, thread them onto a bolt, and you have a backup with no battery, no screen, no ink, and no company that has to still exist in ten years for it to work.

The jig is a two-piece 3D-printed fixture. A base holds the washer flat and square; a guide holds the letter punch vertical over the right spot. That is all it does, and that is the whole point — it is the difference between letters that line up and letters that wander.

Designed by BlockMit — we just print it

The BlockMit washer jig is the work of the Blockmit project, published free at Thingiverse thing:4590734 under the Creative Commons Attribution 4.0 licence. We did not invent it. We print it in Montreal, and we have adapted the original to a second washer size so that Canadians can finish the build with parts they can actually buy — that change is ours, the design is theirs. If this jig protects your seed, read their guide and, if you can, send them sats.

“Blockmit washer jig” by blockmit is licensed under CC BY 4.0. Modified by D-Central Technologies: a second body sized for the imperial 1 inch washer. Printed and sold in Montreal, Quebec.

Two versions. Thirty seconds to pick the right one.

Measure the outside diameter of the washer you can actually buy. Not the hole — the outside edge, straight across.

• 25.4 mm, a clean 1 inch — you have a USS 3/8 inch or a 1 inch fender washer. Choose Imperial.
• 24 mm — you have a metric DIN 9021 / ISO 7093 large-series washer. Choose Metric.
• 16–17 mm — that is the ordinary M8 washer. Wrong washer entirely: a BIP39 word will not fit on it. Go back for the large series.
• Anything else — do not force it. A washer that will not seat square gives you crooked letters.

No washers yet? Choose Imperial. This is the part that surprises people, so we will be blunt about it: the 24 mm metric washer is Blockmit’s original spec, and it is not stocked by any Canadian big-box retailer. It is a fastener-distributor item — Spaenaur, Fastenal, Forces Inc — usually sold a hundred at a time. The imperial 1 inch washer is on a peg hook at Home Depot, Rona and Canadian Tire this afternoon. If you want to finish this build today, imperial is the one that lets you.

The two are not interchangeable, and we are not going to pretend otherwise. 24.00 mm against 25.40 mm is a 1.40 mm difference, which is 0.70 mm of radial slop in the pocket. The washer walks under the hammer and your line of letters goes crooked. No single jig serves both. That is the entire reason there are two.

One near-miss worth knowing before you buy: Princess Auto’s Metric Large Penny Washer Kit is the only large-metric option in Canadian retail, and its M8 washers are 25 mm across and 1.5 mm thick — not 24 × 2.0. They will not fit the metric jig, and in the imperial pocket they sit loose. Skip it.

Specifications

Imperial version (SKU DC-TOOL-BLOCKMIT-I) — takes a 1 inch (25.4 mm) outside-diameter flat washer: the USS 3/8 inch or the 1 inch fender washer. Note that “1 inch washer” covers three different parts with three different holes (11.13, 7.14 and 5.56 mm), so match your bolt to your washer’s hole — an M8 bolt will not pass through a 1/4 inch fender washer.

Metric version (SKU DC-TOOL-BLOCKMIT-M) — Blockmit’s original spec: an M8 large-series washer, 24 mm outside diameter, 2 mm thick, standard DIN 9021 (identical to ISO 7093-1). This is not the ordinary M8 washer, which is only about 16 mm across and far too small to stamp a word on. Ask for the large, fender or penny series and say “24 millimetre” out loud, because the standard number is what stops you going home with the 16 mm ones.

Both versions:

• Punch character size: 3 mm (1/8 inch). That is the height of the letter it stamps. Eight characters have to fit around the washer, and BIP39 words are never longer than eight characters.
• Punch shank: approximately 6 mm. That is the square steel bar you hold and hit, and it is the only dimension the jig actually grips.
• Two pieces: a base that seats the washer, and a guide that holds the punch vertical.
• Material: 3D-printed plastic. Made to order in Montreal, Quebec.

Read the punch spec twice — this is the most common ordering mistake

A letter punch has two completely different dimensions, and the number on the box is not the one the jig cares about.

• Character height is the size of the letter. This is what the box advertises. You want 3 mm / 1/8 inch. A 6 mm letter set cannot fit eight characters around a 24 mm washer, and no jig can fix that.
• Shank is the square bar you hold. This jig takes roughly 6 mm. It is set by the punch line’s duty class, not by the letter size — a 3 mm and a 5 mm set from the same maker often share one bar.

Most vendors never publish the shank dimension. Measure the bar with a caliper before you buy. One warning worth the trip it saves you: Lee Valley’s 3 mm letter set (92W6820) has the correct 3 mm characters but a 5/16 inch (7.9 mm) bar, which is too large for this jig’s guide. Check the bar, not the box.

What you also need — we do not include these

• Washers to match the version you chose — one per word, so 12 or 24. Stainless, A2/304 or A4/316. Not zinc-plated, not galvanized. See below for why.
• 3 mm (1/8 inch) letter punches, A–Z and 0–9. You buy these once and they outlast the jig, the washers, and probably you. Spring-loaded “automatic” punches are a different tool and will not work here.
• A stainless bolt and nut to hold the stack in order. Blockmit’s guide specifies an M8 A2-70 stainless screw and an M8 wing nut. Twenty-four DIN 9021 washers stack to roughly 48–53 mm, so an 80 mm bolt leaves comfortable margin — that length is our own calculation, not upstream’s.
• A mallet and a steel block or anvil underneath. A wooden bench absorbs the strike and gives you letters too shallow to read. Upstream’s own tip: double-sided tape on the block to stop the jig and washer moving.

All of it is standard hardware-store and industrial-supply stock. Our own tools category has the rest of the bench kit.

Straight talk about fire

The jig is plastic. It is a tool, not the backup — you use it for an hour and put it in a drawer. The backup is the steel washers you stamp with it.

And the steel you choose matters more than anything else on this page. Zinc plating melts at 419.5 °C. A house fire reaches flashover between 500 and 600 °C. A zinc-plated or galvanized washer comes through the fire as bare steel — and stamping has already broken the plating anyway — then meets the water the fire crew puts through the room, and starts rusting. The letters stay readable for a while. “A while” is not what a seed backup is for.

Buy stainless. A2/304 melts at 1400–1450 °C and A4/316 at 1375–1400 °C, well clear of any residential fire. A2 and 304 are the same steel under two naming systems, as are A4 and 316. Match your metals: stainless washers get a stainless bolt and nut, because zinc is anodic to stainless and a plated bolt in a stainless stack will corrode away first.

We have not burn-tested this jig or any washer, and we are not going to pretend we have. The figures above are published melting points and published fire-science numbers. This method has not been independently stress-tested by any third party, and we make no fire, flood or crush claim for the jig or for the parts you buy to go with it.

What this is not

• Not the easiest way to mark metal. Stamping is the least forgiving method — you are swinging a hammer and there is no undo. The jig exists precisely because freehand stamping goes crooked: holding a punch perpendicular to a small round washer while you strike it is genuinely hard. The jig removes most of the ways that goes wrong. Not all of them.
• Not a secrecy upgrade. A stamped washer is exactly as readable to a thief as paper. Metal solves durability. Secrecy is a passphrase, a location, or splitting the backup.
• Not permanent, as a tool. The jig is a consumable. A full 24-word phrase is a couple of hundred hammer strikes. If you plan on two or three backups, order two jigs.
• Not the whole job for every wallet. If you use multisig or a non-standard derivation path, the words alone will not restore your funds. You need the descriptor too.

Practise first

Steel has no undo. Before you touch your real words, do a full run on scrap washers with a throwaway phrase. Never photograph, type, or hand around your real seed to rehearse with — the point of a practice run is that nothing about it matters.

Why buy it from us

You could print this yourself. The design is free and open, we have linked it above, and if you own a printer you do not need us at all — that is how it should be. What we sell is not owning a printer, not tuning a first layer, and not fighting warp on a small flat part. Ours ships from Montreal, so you are not waiting three weeks or paying duty.

There is one more reason, and it is not ours. Jameson Lopp, who has stress-tested more than seventy metal seed storage devices, recommends DIY approaches to privacy-minded people on the grounds that you should assume shipping information leaks. A generic jig and a bag of hardware-store washers say nothing about you. A branded seed vault delivered to your door says quite a lot.

Get your words off paper.