Page 8-2 of the RV7 assembly manual tells the builder to fabricate a set of 1 7/16 (1.4375) spacers to properly space the parts of F704 center section so that the Wing spar can fit inside.
If this space is too small, you will have a very difficult time installing the wing. The problems of a space that is too small may be as sever as impossible to install or galled mating surfaces. Most spar stubs I have measured are greater than 1.438 thick.
We recommend that you clamp the pieces of your wing root together and measure it with an accurate calipers or micrometer. Select spacers that are no less than this measurement to no more than about .003″ greater.
Our spar spacer set is a matched (+/- .001) set of steel tubes that have parallel ends.
They have an inside diameter of .438 and an OD of .750.
While we make these in a range from 1.438 to 1.447, only the ones that are in stock will show up on the drop down list.