4" long Light weight Titanium spacer material.
Links to Tools for cutting tube:
Master Plumber 745122 5/8 To 2-1/8-Inch Large Pipe Tube Cutter
RIDGID 31632 Model 151 Quick-Acting Tubing Cutter, 1/4-inch to 1-7/8-inch Tube Cutter
*Support the inside of the tube with a socket wrapped in masking tape