20X1 3/8 (37-451) Inner Tube with Schrader Valve

20 x 1 3/8 inner tubes are also commonly known as 37-451

451mm is the measurement across the rim, bead to bead and 37mm is how proud the tyre sits off the edge of the rim.

Before installing inner tubes run your hand around the inside of the tyre to ensure your tyre doesn't have any stones or sharp objects that may puncture the brand new inner tube. If you decide to use objects to help fit inner tubes please ensure only blunt objects are used due to the fragile nature of the inner tubes. Using sharp or metal objects will pinch, puncture or pierce inner tubes.