Specifications:

• Shimano Ultegra Cassette 6600
• CS-6600
• 10 speed
• Steel cogs
• 11-12-13-14-15-16-17-19-21-23T
• Shimano HG Freehub 
• Approx Weight (w/ lockring): 249 g
• NOS, new Shimano cassette in original box. May have some minor evidence of shelf wear from storage, though there appears to be none of note.