Specialized Insulator Mitts OSFA These mitts are designed to work with mountain bike bars, more specifically for use with fat bikes, and they easily secure via a simple-to-use attachment at the bar ends. The closures, meanwhile, are fully adjustable, so you'll be able to lock-in the warmth once you get the blood moving on your ride. And as a result, these mitts create an extremely warm and comfortable microclimate that's all but entirely shielded from the cold.