Two identical coaxial coils of radius $R$ separated by distance $R$ (equal to radius) carrying current in the same direction create a nearly uniform field in the region between them. At the midpoint: $B = \frac{8\mu_0 NI}{5\sqrt{5}R}$. This setup is used in laboratories to produce uniform fields. The uniformity arises because the first derivative of $B$ with respect to position vanishes at the midpoint.