Size Fitting· - Wood or Composite Posts : must be smaller than 3-13/16" square· - Hollow Vinyl Posts : inside opening must be larger than 3-15/16" square Product Features 100% brand new and high quality· Sun Powered· No Wiring· On/Off switch· Ultra Bright LED· Powered by the sun· Fast & easy install· Rechargeable Ni-Cd AA battery included· Energy, electrical saving· Ideal for areas where conventional electrical supply is not available· - User controllable on / off switch· - CE Certified for ultimate safety· - Upper Base Dimensions : 4" (l) x 4" (w)· - Lower Base Dimensions : 4" (l) x 5.5" (w)· - WILL FIT 4" x 4" POSTS· Solar Light Dimensions : 5.5" (l) x 5.5" (w) x 4.5" (h)· One High output long lasting ultra-bright white LED bulb· More expensive ultra-highly sensitive solar panel usually seen on calculators is used· Automatic dusk-to-dawn operation, On/off manual over-ride switch· Recharged by solar panel under sunlight· Light turns on automatically when dark· Safe Water Resistant· Corrosion resistant