PC Sync Cable For Flash
This comes by default with the DropRobo kit, any additional can be bought here. This connects with the flashes having PC Sync Port. This is a PC-3.5mm to 3.5mm 2 pole audio male jack. of about 30 cm length. If your flash does not have PC Sync port then you'll have to get a hotshoe adaptor with PC Sync port and a chord for the hotshoe.