The Background button icon set contains 690 empty buttons with different sizes, colors and shapes. The images are made available in the PNG format.
An Icon set contains, if not differently given:
Windows 7 / Vista / XP Icons (an Icon contain 14 Icon formats, The format 256*256 RGB/A is for compatibility reasons uncompressed) Icons for Windows 95, Windows 98, Windows Me, Windows NT, Windows 2000 The file formats BMP (24 bit), PNG (32 bit) and GIF (8 bit) in the dimensions 16*16, 24*24, 32*32, 48*48, 64*64, 128*128 and 256*256 pixels The vector icon sets contains in addition the file formats AI, SVG and PSD The vector icon sets of Icons Bundle contains in addition the file format XAML for WPF.