A bison tube is a small, metal, water-tight cylindrical container that can be used for micro-caches. These containers are usually small enough to fit on a keychain, and were originally designed to hold pills. The name is derived from the company which manufactures most of these types of tubes, Bison Designs.
Available sizes include:
- 2⅜ x ⅝ in / 60 x 16 mm (Small)
- 2¾ x ⅝ in / 70 x 16 mm (Large)
- 2 x ¾ in / 50 x 20 mm (Scuba Tank or Micro-Cache Capsule)
- 3 x 1 in / 75 x 25 mm (Extra Large)