Take a look at the Spinelock review by bikepacking.com
Sizing

There are two size options, neither of which sacrifice features for capacity. The smaller but largely versatile Spinelock 10L maximizes your carry with minimal tyre clearance and provides a generous amount of waterproof storage with additional space on the external corded deck. If you are going on a long expedition or carrying cold weather gear we recommend checking out the Spinelock 16L.

The 10L Spinelock requires 20 cm tyre clearance and 16.4 cm exposed seat post
Features

• Innovative Spinelock stability system completely eliminates side to side sway
• Waterproof construction
• Two mounting positions to accommodate seatpost setback and saddle adjustments
• A low profile, high strength, forged aluminum clamp works in combination with precision IGUS bushings to form a quick-release pin interface making bag removal a cinch
• Quick release bag from bike
• Internal HDPE plastic structure
• One way, low profile, air purge valve
• Carbon seatpost friendly
• Hypalon slots for a rear light
• Top mounted external webbing and bungee for additional storage
• Protective external plastic bottom frame sheet
• Active cam buckles prevent side straps from slipping on rough terrain
  

Fit

• Traditional saddle style rails are required.  Does not work with most Brooks saddles. Does not work with most Brooks saddles including (B17, B66, B67, Flyer, and similar). Spinelock is compatible woth Brooks Cambium line (C15, C17, C19).
• Minimum 20 cm tyre clearance and
• Minimum exposed seat post 16.4 cm
  

Important information on use and fit

• The Spinelock bag is not compatible with carbon fiber saddle rails
• Only compatible with traditional style saddle rails and is not compatible with most models of Brooks saddles including (B17, B66, B67, Flyer, and similar), Spinelock is compatible woth Brooks Cambium line (C15, C17, C19).
• This product is not designed for use with dropper seatposts
• This bag is for carrying soft, pliable objects. sufficiently pad any hard edge objects like cookware to prevent premature wear
• It is mandatory to check tyre clearance prior to use, especially with full suspension bikes. Bag contact with a tire can cause a bad wreck and ruin your day. Tyre damage to the bag is not covered by warranty
• A Torx-25 wrench is needed for installation. You likely already have one on your multi-tool!
  

Specifications

Weight:  638g
Volume:  10L
Materials:  210 Denier Ripstop Nylon with dual coated TPU, urethane based Hypalon reinforcement fabric, UV-stabilized, impact resistant nylon resin, forged aluminum. Imported.