This listing is for two CNC billet velocity stacks with 3 grub screw fixings.Internal diameter of stack is 50.5 MM , this is the stack to carb fitting where the 3 grub screws on the stack are located. Overall length of stack is 45mm. Maximum external diameter of stack is 77mm, this is the flared end of the stack. Have fitted 4 of these stacks to one of our race bikes and found an immediate power increase of 5 bhp when tested on the dyno. Sold individually to suite your needs, see other listings. price includes free postage, package and insurance to uk mainland, but excludes Scottish Highlands and Islands. Please message for all other postal area charges. World wide shipping available through EBay Global Shipping Program . Please see my other items for variation in colours. LAST PAIR LEFT, WHEN THESE ARE GONE THEY WILL NOT BE REPLACED !