Odin Works M-LOK to Arca Conversion Rail, 9, Matte Finish, Black ACC-ML-ARCA-RAIL-9 The ARCA rail was designed to give you the flexibility and ease of use that you need for mounting your rifle. This rail system is commonly used for mounting Arca Swiss style tri-pods but it also can be used with Arca Swiss style bi-pods too" making tri-pods and bi-pods easy to switch back and forth between. We've all been there" having to take off a bi-pod mount and switch to a tri-pod mount at the most inconvenient time. Now" the ARCA rail system is your all in one solution to mounting your rifle" no hassles guaranteed.