The 12x Chorus cassettes for use with the disc or rim brake groupset.
The Chorus groupset is fully compatible with the cassettes from the Record and Super Record 2x12-speed groupsets (11-29 and 11-32) but also introduces a new cassette specification of 11-34.
The 11-34 cassette offers cyclists even more versatility and a greater choice and autonomy in terms of available gears. 
Chorus 12-speed now therefore offers a total of three cassette options:

11-12-13-14-15-16-17-19-21-23-26-29
11-12-13-14-15-16-17-19-22-25-28-32
11-12-13-14-15-16-17-19-22-25-29-34

Technologies

Same width as the 11-speed cassette: Totally compatible with wheels and frames.
The two bigger sets of three in a single-block piece: It eliminates energy dispersion.
Surface treatment: It increases durability and improves smoothness
Same-thickness spacers: Ensures error-free fitting

Features and Benefits

Compatibility: Same width as the 11-speed, no need to change or update wheels
Smaller spaces: Faster, more precise shifting
Same spacers: Easy error-free fitting.
Sets of three in single-block steel: Stiffness and elimination of power dispersion
25-29-34 set of three available as a spare part, 
Can be converted from the 11-32 cassette

Weight: 306g (11-29 version)