B . a b . s . f specification for steel hexagonal - headed bolts b . a . and b . s . f threads with close tolerance shanks for aircraft 飞行器用紧公差螺杆的钢制六角头螺栓
2.
B . a b . s . f specification for cadmium - plated steel hexagonal - headed bolts b . a . and b . s . f . threads with close tolerance shanks for aircraft 飞行器用紧公差螺杆的钢制镀镉六角头螺栓