IT grades from IT5 to IT12, what each costs, and how to pick the loosest grade that works.
This is written for buyers and design engineers rather than machinists. It covers what to put on the drawing, what it costs, and the mistakes that turn a straightforward part into an expensive one.
The rules that matter
- At 50 mm diameter: IT7 is 25 um, IT8 is 39 um, IT9 is 62 um
- Each grade step up roughly halves the cost
- Only the features that mate need tight tolerance
- Blanket tolerances on a title block are almost always too tight
Common mistakes
- Applying +/-0.01 mm to every dimension
- Forgetting that tolerance stacks across multiple parts
Both of these are cheap to fix at the drawing stage and expensive to fix after the parts are cut. If you are unsure which side of the line your design is on, send it over before you release it.
How this shows up in a quote
A quote is built from material, machine time, setup, finishing and inspection. Anything that adds a setup, a secondary operation or a tighter inspection method moves the number. When we quote, we show the process route, so you can see which requirement is driving the price and decide whether it is worth keeping.
Frequently asked questions
Does this apply to both milling and turning?
Yes. The principles are the same. Turning is usually cheaper for concentric geometry and milling for prismatic geometry, but the tolerance and finish rules carry across both.
What is the cost of getting this wrong?
Usually one extra setup, one extra operation or a scrapped batch. In practice, fixing it at the drawing stage costs nothing; fixing it after the first article costs a week and a re-quote.
Can you review my drawing before I release it?
Yes, and we would rather do that than quote a design that is going to be expensive. Send the STEP file and drawing and we will come back with DFM comments alongside the price.
Do you work from a PDF drawing or do you need CAD?
We need a STEP file for the geometry and a dimensioned PDF for the tolerances. A PDF alone is not enough for anything with curved surfaces.
Related pages
- Guides — the full index for this section.
- How to Specify Surface Finish
- Minimum Wall Thickness for CNC Parts
- GD&T Basics for CNC Machining Buyers
- Corner Radius Rules for End Mills
- Instant CNC quote
- Tolerance quick reference
- Frequently asked questions
Get a price for your part
Send a STEP file and a drawing with tolerances, material and quantity. We quote within one working day and machine in our own facility in Shenzhen — milling, turning, EDM, grinding and finishing under one roof, no trading middleman.
Start an instant quote or send your drawings directly. English-speaking engineering support, DFM feedback before you commit to a batch.