Draw the tool, in the manual's style
Father's Day merchandise is built from jokes about grilling and naps. An exploded parts diagram of the thing he actually owns is funnier, more accurate, and gets worn in the workshop.

The Father's Day aisle runs on four jokes: grilling, naps, lawn opinions, and the word dad in a serif. It's a category that assumes it's writing about a type of person rather than a person.
The alternative is to look at what he actually owns.
Why a parts diagram?
Because it treats his thing seriously, and seriousness is the joke.
An exploded technical drawing — every component floating apart along its assembly axis, numbered callouts, a figure number — is the visual language of a manual. Applying it to a hand plane, a specific reel, a carburettor, a particular espresso machine says this object is worth documenting, which is both funny and completely sincere.
It also happens to be the most flattering thing you can say about somebody's hobby: that you noticed it has parts.
Does he have to be into tools?
No — the format applies to any object he's obsessive about.
A bicycle drivetrain. A film camera. A saxophone. A specific model of radio. A gearbox. A bee hive. A chess clock. The register doesn't care what the object is, only that he could name every part of it without looking.
That's the actual test for this gift: does he know it well enough to read the drawing? If yes, it's the right subject.
Isn't this the retirement design?
Related, and pointed at a different moment.
A retirement diagram is about a working life ending — the machine he knew for thirty years, drawn as a record. A Father's Day one is about a thing he chose to spend his weekends on, and it can be much lighter: the ridiculous number of parts in a coffee grinder is a joke, not an elegy.
Same technique, different weight. Worth deciding which one you're making.
What details make it convincing?
Four, and they cost nothing.
- A figure number —
FIG. 4— implying a manual with other figures in it. - Numbered callouts on leader lines, repeated for identical parts.
- A model designation, invented:
MODEL 3150. - Exploded spacing, components separated in assembly order.
Those conventions are what make it read as documentation rather than as an illustration of a tool. They're also what makes it funny — nobody writes a manual for the thing your dad won't stop talking about.
Can I use the real manufacturer's diagram?
No, and you don't want to.
Real parts diagrams are somebody's artwork and they're covered in somebody's brand marks. They're also dense, grey and unreadable at chest size.
A drawing in that tradition, of his object, with an invented model number, is both yours and better — the tradition is free, the specific artefact isn't.
What if I don't know what it's called?
Photograph it. That's enough.
The drawing is made from the shape — the proportions, the housing, the arrangement of parts. A phone photo of the thing sitting on his bench contains all of it, and you don't need to know the model, the year, or what any of the pieces do.
Which is the useful part: this gift requires attention rather than expertise.
Is it wearable, or is it a novelty?
It's the rare Father's Day item that gets worn in the place it's about.
A technical print on a plain garment is workshop-appropriate, weekend-appropriate and unembarrassing in public, because to a stranger it's just an interesting piece of industrial graphics. That's a much longer life than anything with the word dad on it.
How do I get one made?
Photograph the object at JustOG and say it should be an exploded technical diagram. 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.
He doesn't want a joke about naps. He wants somebody to notice the plane has fourteen parts.