Altair 2nm G-Band Solar Contrast Filter filter specifications: 

• Standard 1.25" Filter Threaded Aluminium Cell
• CWL 430.3nm @ 96% transmission, tolerance 1%
• FWHM 2nm, tolerance 0.5nm.
• 1.85mm thick quartz ?/4, Parallelism (arcsec) 30"
• Si02 "hard" overcoat with UVIR Block 300-1100nm and Anti-Reflection Coating
• High resolution spectrographic test report included corresponding to each individual filter.