18BG401 up for sale is a fuel and oil resistant flange gasket used for a military application but can work for many other uses , the OD outer diameter is 6 5/8 x just under 4 ID inner diameter the bolt hole pattern lays at about 5 1/2 x just over 1/2 holes 6 holes , the thickness is 0.026 inch , nice gasket for many uses related to fuel oil and other fluids , comes as shown in photos , we opened one up for photos the rest are still sealed ,