Jack

The jack is the business end of the instrument. You can see the tongue from the back, with its nylon (used to be boar's bristle) spring, the back of the plectrum, and the back of the felt damper which stops the string sounding when the jack is at rest. Jacks are fiddly to make. There are about 256 of them in a 3-register instrument, and about 13 different operations to complete on each jack. Unless you are a purist it makes sense to buy these from someone who specialises in making them