This is a very rare DECCA FFSS CARTRIDGE ADAPTER D3, a dedicated adapter for DECCA cartridges. It's used to adapt DECCA cartridges, such as the Mark 1 to III, and some of the IV series, for use with standard universal tonearms. It's a really old item, so I don't remember exactly, but I had several, so it's probably unused or in near-mint condition, having been installed only once. #MC Cartridge MC Cartridge #Step-up Transformer Step-up Transformer #Turntable Turntable #Analog Record Analog Record #Cartridge Record #Tonearm Cartridge #Record Phono Equalizer #Phono Equalizer Tonearm #Audio Audio #Headshell #Lead Wires #Conversion Adapter #Decca #DECCA Conversion Adapter #DECCA