The Robert Axle Project makes 12mm thru axles for bike trailers, trainers and accessories to make your best bike fun and functional. Our products allow cycling families, adventurers, commuters and enthusiasts to enjoy traveling by bicycle without leaving their cargo behind. With our thru axles, you can attach your favorite bike trailer—Burley, Chariot, Thule, BOB and more—to any bicycle that has a 12mm thru axle. We have 12mm thru axles that fit mountain, fat, road, cross, and electric bikes. Your Best Bike. Your Best Adventure.