What is the difference between GY8 and G8 base

G8 and GY8 light bulbs are bi-pin bulbs with a gap of 8mm (millimeters) between the pins. 
The difference between G8 and GY8 bulbs is the pin length.
G8 Bulbs - pin length is 8 mm, whereas the GY8 pin is 8.5mm.
The pin thickness is the same as 1 mm for both G8 and GY8 bulbs.
For most applications, the pin length will not make a difference and you can use either G8 or GY8 bulb.