A Sea&Sea Knob gives you the control you need when adjusting the levels on your Sea&Sea YS-D3 Mark 1 strobes. Perfect for those in temperate waters as it make adjusting the levels a snap with gloved hands. The Mode/EV Knob presses onto your existing knob and is secured using a small set screw. The Mode/EV Knob is constructed of durable impact resistant Red plastic. This knob is for 3-spoke knobs on the Sea&Sea YS-D3 Mark 1 Strobes. There are no markings for Mark i, Mark II has is written below 'Lightning'