2.5~4mm, 4mm is the standard of Yamaha. Usually, Yamaha's piano will be less than 4mm, and 2.5mm means that the distance from the lower edge of the 6 strings to the upper edge of the product at 12 can not be less than 2.5mm under standard tuning.
Generally, the height of a piano will not be higher than 4mm, except for some pieces of waste wood without steel bars in the piano or the piano with no adjustment at the neck depression. However, a large number of domestic miscellaneous brands deliberately reduce the chord distance to deceive consumers, resulting in the illusion of good feel, not only poor sound quality and intonation, but also easy to cause jumping.
It's just that many pianos don't master the correct string pressing skills, so they blindly seek low chord spacing. If you are interested, you can go to Youku to see Master Ulli's tutorial. Remember that the previous sections will talk about the basics of pressing strings. In fact, it only takes a little effort, and the appropriate chord distance is the guarantee of timbre.