The Mason Pearson Pocket Sensitive Pure Bristle SB4 Dark Ruby is a prestigious hair brush that's excellent for anyone with very fine or thinning hair. The small size of the Mason Pearson Pocket Sensitive Pure Bristle SB4 Dark Ruby makes it ideal for fine hair or younger hands, as well as making it travel friendly. Using the classic Mason Pearson design of all their brushes, the SB4 is an iconic brush. Gently pass through your hair.