In daily engineering drawing, many users like to quote such as "un-note tolerance according to ISO2768-m", then what is ISO2768 standard?
A thousand words are summarized into the following table:

Limit size of length and angle dimensions
According to ISO 2768-1
Nominal size	Tolerance size
range	f (fine)	m (middle)	c (Crude)	v (Very thick)
mm	Tolerance mm	Tolerance mm	Tolerance mm	Tolerance mm
0.5-3	± 0.05	± 0.10	± 0.15	–
3- 6	± 0.05	± 0.10	± 0.20	± 0.50
6- 30	± 0.10	± 0.20	± 0.50	± 1.00
30- 120	± 0.15	± 0.30	± 0.80	± 1.50
120- 400	± 0.20	± 0.50	± 1.20	± 2.50
400- 1000	± 0.30	± 0.80	± 2.00	± 4.00
1000- 2000	± 0.50	± 1.20	± 3.00	± 6.00
2000- 4000	–	± 2.00	± 4.00	± 8.00
Limit the size of the angle size
According to ISO 2768-1
Nominal size	Tolerance size
range	f (fine)	m (middle)	c (Crude)	v (Very thick)
mm	Tolerance mm	Tolerance mm	Tolerance mm	Tolerance mm
<10	± 10′		±1°30′	± 3°
10- 50	± 30′		± 1°	± 2°
50- 120	± 20′		± 30′	± 1°
120- 400	± 10′		± 15′	± 30′
400 以上	± 5′		± 10′	± 20′
Bending radius (curvature) and the ramp height (angle) of the limit size
According to ISO 2768-1
Nominal size	Tolerance size
range	f (fine)	m (middle)	c (Crude)	v (Very thick)
mm	Tolerance mm	Tolerance mm	Tolerance mm	Tolerance mm
0.5-3	± 0.20		± 0.40
>3-6	± 0.50		± 1.00
>6	± 1.00		± 2.00