USA Industrial Tool · Blog
What +.0003 / −.0000 means, and why it matters to our long-term customers
Our custom tools are held to +.0003 / −.0000 in. A tool can be up to three ten-thousandths of an inch over the size on your print. It is never under.
How to read a tolerance
A tolerance says how far a finished tool is allowed to be from the size on the drawing. A common band on general-purpose tooling is ±.0005 in. That is respectable, and plenty of good work runs on it.
It also means a tool can arrive five tenths over or five tenths under. (A "tenth" in a machine shop is one ten-thousandth of an inch.) The total spread is .0010 in., so two tools from the same box can differ by a full thousandth.
Where our tools land
We hold +.0003 / −.0000 in. The spread is .0003 in., less than a third of the ±.0005 band, and all of it sits on the plus side. The tool is at size or a hair over.
Why the minus side is zero
A cutting tool only gets smaller as it wears. A tool that starts undersize has given up part of its working life before the first cut. A tool that starts at size, or slightly over, gives you the whole run.
It also makes tool changes predictable. When the tolerance only goes one direction and the band is narrow, the new tool measures like the last one did when it was new. Offsets set for one tool hold for the next.
How we check it
A tolerance is easy to print on a quote. Holding it is the hard part, and you only know you held it if you measure.
Every custom tool we supply is measured before it ships. The measuring is done in a clean room, because at this scale dust on a surface is enough to throw off a reading. The instruments are calibrated and carry their calibration stamps.
A lot of people buying tooling do not know this step happens. It is the reason we can put a number like +.0003 / −.0000 on a tool and stand behind it.
Why it matters on a reorder
Most of our customers are aerospace, dental and medical manufacturers who buy the same tool again and again. For them, the first tool being right matters less than the two-hundredth tool being the same as the first.
That is what a tight, one-sided tolerance buys you: the tool you receive next year measures like the one you received this month.
Have a tool you reorder?
Send us the print and your usage. We will quote it for your quantities.