Holder for two Microsync Digital transmitters. They discharge the battery if the base contacts are bridged. Considering they don't come with a cover or holder, it's an issue to deal with. They are tiny and easily lost so I made the holder for two and put a ring on it for a ball chain or tag to keep them from getting lost.Use DuoSmdock3.skp and add your own return info on the faces in case you lose it... or use DuoSMdock2.stl or svg and you will have my contact info on it so when you lose your Microsync transmitter it will be sent back to me?Only have one? cut it in half and just have a holder for one... have four transmitters? Not a tough mod.... I haven't put anything in the keyring hole yet but it may be a bit fragile.