Neewer Compact Lightweight Portable External Battery Pack Replacement for Nikon Speedlite Flash SB910 SB900 SB800 and Neewer 561,562,660III,NW910/MK910,NW580,NW670/VK750 II,NW690 Designed to boost the recycling speed for your flash in a much more effective and economic way. Red light indicator for working status. Smart 1/4" screw knob design for mouting the battery pack beneath your DSLR camera.Do not force the screw knob through the hole.You need to spin the screw in for the hole to hold it. No complex operation needed. Easy to use. Suitable for Nikon Flash SB-II,SB20,SB24,SB25,SB26,SB27,SB28/28DX,SB800 SB910 SB900 Neewer 561,562,660III,NW910/MK910,MK900,NW580,NW670/VK750 II,NW690/MK950II