These single block holders are designed to hold a single router bit with a spot for a label.

There is a model available for 1/4", 1/2" and 8mm shank router bits.

I am not a woodworker and don't use my router bits often, so I found it worthwhile to sacrifice a bit of storage density to be able to easily identify each bit.

If you are better than I am at identifying bits at a glance, and would prefer something that stores more bits in less space, take a look at this router bit caddy by Zwierzak