Their movement is Shanghai 8120 manual movement, and the bottom cover is a transparent bottom cover.
SPECIFICATIONS
Movement: Mechanical. Hand wound. Case Material: Stainless Steel 316L Case Diameter:36mm Case Thickness:11mm Weight:36g Band Width: 19mm Band Material:Nylon Crystal: HardlexGlass Features: Retro look. Mechanical movement. Water Resistance Depth: None.