This 'big bros' article is part of the book - Trad Climbing Basics.
Big Bros are expandable tubes which protect wide cracks. They are lighter and more compact than large cams but are harder to place, cannot be shuffled up the crack and do not work as well in flares.
Once expanded into the crack, one side of the big bro will be higher up than the other. When the higher side is weighted (e.g: if the climber falls), the unit becomes wedged into position.
Placing Big Bros
Find a flat spot in a parallel sided crack. Place the inner tube against the wall.
Press the trigger button and let the tube expand slowly to fill the crack (it can damage the big bro if you push the button and let the tube slam into the rock).
The inner tube should contact the rock at a lower point than the outer tube. Wiggle the tube around a little to get the best fit.
Spin the locking collar to the end of its range and tighten it. This sets the big bro in position.
To get the best fit, wiggle the tube slightly as you fasten it.
Removing Big Bros
Spin the collar to the end of the tube and compress the big bro until the trigger pops back into to place.
Racking Big Bros
Big bros should be compressed and racked on their own separate carabiner.