The Medium Saddlebag is the "jack of all trades" of saddlebags. It shares the same tried-and-true construction as the Large, but modified to accommodate saddles with or without bag loops: it is tapered to a much narrower dowel at the saddle attachment point, and the two grommets for the attachment straps are positioned halfway between the spacing of typical bag loops on old-style leather saddles and the spacing of saddle rails on typical modern plastic saddles. The rest of the bag flares out from that attachment point so that it still gives you plenty of capacity.
The Medium is more squat in proportions than the Large and the Small, with more of the bag's capacity resting above the attachment point, giving it the most clearance above the rear wheel of the three. Additionally, the lid panel wraps around the bottom to buckle securely with two straps near the center, so that you can cinch it tight in the center and be sure it won't drag on the tire even if your saddle is relatively low.
It is 5" wide at the point where it attaches to the saddle and tapers out to 10" wide on the bottom and rear (not counting side pockets); about 8" from front to back at the widest, and 7" high from the bottom to the top edge of the lid when the lid is closed. Its capacity when more or less full but not stuffed is about 5 liters or 305 cubic inches not counting exterior pockets, although you could probably get another liter's worth of stuff in there and still close it. It requires about 7" of clearance between wherever it attaches and the rear wheel although you can get away with a bit less if you cinch down the straps tightly or use a rear fender.
Like the Large, the Medium Saddlebag has a choice of where to strap down the bottom, so that whatever your setup or geometry you can keep the bag from swaying.
Depending on the geometry of the bike, saddle, and riding position, some riders find that with traditional saddlebags mounted directly to bag loops (or saddle rails, in the case of the Medium) and seatpost, their legs hit the sides of the bag when they pedal. If this sounds like you, check out the Dill Pickle Gear Tool Canister, which keeps your bag off the back of your legs and also keeps your tools conveniently accessible whether you're carrying your whole saddlebag or not.
Available options for the Medium Saddlebag include:
• Side Pockets: Either nylon mesh or Cordura
• Mesh Lid Pocket: Either nylon mesh pocket on the lid, or two sets of D-rings for lashing down a pump or extra jacket, etc.
• Rear Zip Pocket: Zippered 3-D pocket on the back of the bag for stuff you'd like access to without pawing through everything else. NB: This does make the back of the bag a little wider, so if you have especially low clearance over your rear tire, you probably don't want this option.
• Wallet/Brevet Card Pocket: Zippered pocket inside the lid to keep small items like your wallet and brevet card clean and dry.
• Interior Mesh Pockets: Choose a single center pocket, two side pockets, or both, to help organize your stuff inside the bag.