Emerson replica tone caps are painstakingly handcrafted, using highly-sought "new old stock" paper-in-oil Soviet military surplus capacitors.
.050uF - 150V
Single-coil guitars, many basses
.100uF - 150V
Basses and certain eras of vintage Fender guitars
Capacitors are energy-storage devices that filter the high frequencies. A cap lets the tone control roll off the treble response, progressively warming the tone. The higher the value, the more bass output from the tone control at its "zero" setting.