The Wheels Manufacturer BB30 Outboard Thread Together bottom bracket is specifically designed for use with 24 mm spindles in frames with 42 mm shell internal diameter without needing an adapter.
Features
Compatible with BB30 and Specialized Alloy OSBB bottom bracket/frame interfaces and 24 mm diameter crank spindles, such as those from Shimano
Fits frames with 68 and 73 mm shell widths; 42 mm shell internal diameter
Machined aluminum cups thread together for stability, increased bearing life and simpler installation/maintenance