Orvis Posigrip Threader Fly Box -Medium is a little bit larger than her sister box- the Small model. lt is perfect to store and carry dry flies, small streamers, wet and nymphs. Enough for a fishing day. Like all Orvis Threader fly boxes, this model has a nice cream/gray color, easy to notice if you forgot it on the river bank.. The Posigrip type of fly is designed to have a classic look but to modern and function at interior.