敲击法用应购件与一对应件（可用换出来的旧件，也可用不同厂家的同类件）互相撞击，留有痕迹的一件视为硬度较差。 听声法两手各拿一件欲购的不同厂家的同类配件，无两个厂家配件时，可用原换出的旧件，两件适当用力互相敲击，也可把两个对比件同时抛在硬地板上，听其声音，发 Percussion method should be purchased with a counterparts (available for replacement of the old pieces, also available from different manufacturers of the same type) collide with each other, leaving a trace of the less hard. Listen to both hands with the acoustic method to buy a different manufacturer of similar accessories to buy, no two manufacturers parts, the original can be used to replace the original pieces, two pieces of the appropriate force each tapping, but also the two contrast at the same time throwing Hard on the floor, listen to their voice, hair