Hobnail: What Fits & When

Something in your home needs a new part. You know roughly what — a filter, a bulb, a blade, a cell. What you cannot remember is which one actually fits.

Hobnail is the notebook for that. Record the exact specification of every replaceable part in your home once, and never work it out again.

WHAT IT REMEMBERS

For each part, Hobnail keeps the details you need at a shop counter:

• The manufacturer's part code
• The size or rating — "10 inch, 5 micron", "9 W, 2700 K", "AA, 1.5 V"
• How it fits — "B22 bayonet", "standard 10 inch housing", "1/4 inch push-fit"
• How many one replacement takes, because a three-lamp fitting takes three
• The brand that worked last time, where you bought it, and what you paid

THE SPEC CARD

Tap any part for a full-screen, high-contrast card with everything on it. Hold it up at the counter. That is the whole feature, and it is the reason the app exists.

THE SHOPPING RUN

Everything overdue or due soon becomes a buy-list, grouped by part type, with every specification attached and an estimated total from the prices you last recorded. Share it as plain text to anyone doing the shopping. When you get home, mark the run as bought and every replacement is logged in one action.

IT LEARNS HOW LONG THINGS REALLY LAST

Manufacturers quote optimistic service lives. Hard water eats a sediment filter faster; a spare-room bulb outlives its rating. After a few logged replacements, Hobnail compares what actually happened in your home against the figure you entered, and offers to correct it.

WHAT IT COVERS

Water purifier cartridges. Cooker hood and chimney filters. Air purifier cartridges and pre-filters. Light bulbs and tubes. Batteries in clocks, remotes, scales and doorbells. Vacuum belts and brushes. Trimmer and mower blades. Washing machine inlet seals. Tap and shower cartridges. Fuses. Printer consumables. Mop heads, filter pads and wicks. Anything with a specification and a replacement.

Parts that only fail rather than wearing out — a fuse, a cracked seal — can be marked "only when it fails". They never go overdue; Hobnail simply keeps the spec so you can buy the right one the day it goes.

BUILT TO BE PRIVATE

• No account, no sign-up, no email address
• No adverts, no analytics, no tracking of any kind
• No internet permission — the app cannot send your data anywhere, by design
• No permissions at all. You will never see a permission dialog.
• Everything stays in the app's own storage on your phone

Back up whenever you like to a plain, readable JSON file you choose the location of, through the standard Android file picker. Import it on a new phone. Erase everything in two taps.

DESIGNED, NOT ASSEMBLED

A warm brass and paper palette with a proper dark theme. Part codes set in monospace so they read as data. Original illustrations. Optional Material You wallpaper colours on Android 12 and later.

Works on Android 8.0 and later. Works with no signal, on a plane, in a basement, forever.

Hobnail does not tell you how to replace anything. Follow the manufacturer's instructions, and get a qualified person in where the job needs one.