The PCB Gerber format is an open 2D binary vector image file format. It is the standard file used by printed circuit board (PCB) industry software to describe the printed circuit board images: copper layers, solder mask, legend, etc. PCB Gerber files should be inside a .rar or.zip archive with standard file extensions:
Extension Layer
pcb name.GTL Top Layer Copper
pcb name.GTS Top Solder mask
pcb name.GTO Top Silkscreen
pcb name.GBL Bottom Layer Copper
pcb name.GBS Bottom Solder mask:
pcb name.GBO Bottom Silkscreen:
pcb name.TXT Drills
pcb name.GML/GKO Board Outline
4 layer board also need
pcb name.GL2 Inner Layer2
pcb name.GL3 Inner Layer3
Notes: PCB Gerber file must be RS-274X format. Drill file(pcb name.TXT) should be Excellon format.