The seat barrel bag can be installed on either the bag clips that come standard on a Brooks saddle, or on the saddle rails. Let's look at both.
To begin, open the common sense closure on the front flap.
Inside, you'll find a belt. Unbuckle the belt on the inside.
Un-weave the belt through 3 bag slots.
To install on bag clips, weave the belt from the outside down through the 1st clip on the right.
To install on the seat rails, weave the belt from the outside in around the right seat rail.
Continue to weave into the bag through the 2nd bag slot.
Then weave back out the 3rd bag slot.
And through the left saddle clip from the backside forward if you're using clips...
...or around the left seat rail from the inside out if you're installing on the seat rails.
And finally back into the bag through the 4th bag slot.
Buckle the belt tightly on the inside of the bag.
Lastly, we include an extra stabilizer, a leather cord to help secure it. Tie the leather cord around the seat tube in a knot to provide an extra anchor and increase the rigidity.
That's it! Your beautiful new seat barrel bag is ready to carry the contents of your pockets on the next ride. Ride on.