Many times when I alter kits and have this problem I double tube my blank by taking 1/4 inch masking tape and run it lenghtwise on the smaller tube. Overlap slightly and cover the tube completely. Test fit to see if the smaller tube will now snugly fit into the larger one. If not add another piece of tape until you have the fit you want, than glue the tubes together. Often times I will cut back about an 1/8 inch on both ends of the larger tube and glue on a trim piece on each end drilled to fit over the smaller tube. That way, when you turn down your ends, you will have a solid and neat fit with a little extra material to play with. Don't worry about those tubes ever comming apart, I have yet to be able to get one apart once glued. Jim S