These are tests meant to find the tolerance of your printer. These are the steps you follow to find the tolerance and your different types of fits.
There can be different ranges between the below fits, so it is up to personal preference on how you want your parts to fit.
You will add this amount (Tolerance) to interacting sides of parts.

Realistically, your tolerance should be close to half your nozzle size, and you will have to do this for every nozzle you plan to use with your
printer. A 0.2mm nozzle will have a different tolerance than a 0.4mm nozzle

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Clearance Fit: There is ample clearance (gap spacing between parts) for 2 parts to move past one another (Loosest Fit)
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Transition Fit: There is just enough clearance for the parts to fit into one another and yet still hold together tightly (Both Loose and Tight)
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Interference Fit: You will have to force the parts together (Tightest Fit)
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1. Start with the primary test. This should be 0.10 - 0.60.
2. Test all measurment cubes on the base until you find the one that doesnt fit on it.
3. Once you find the non-fitting tolerance, go up measurments until you find one that fits. (See below: 0.10 doesnt fit but 0.20 fits)
This means your tolerance is between these 2 numbers (0.10 - 0.20 below). You can just say your tolerance is 0.20 or you can go down tighter
the tests.
4. You are now able to go onto the secondary tests between these numbers. Repeat the same step above to find the tighter tolarance. The further
you test down, becomes your new Tolerance.

Ex. Primary Test
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0.10 (No fit)-----
0.20 (Fits)-----
0.30 (Fits)
0.40 (Fits)
0.50 (Fits)
0.60 (Fits)

Tolerance: 0.20

Secondary Test
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0.10 (No Fit)
0.12 (No Fit)----------------
0.14 (Even Tighter Fit)-------
0.16 (Tighter Fit)
0.18 (Fits)
0.20 (Fits)

Tolerance: 0.14

- Silver Harmony Studios

(The print pictured above was made with a 0.4mm nozzle)