For this blade plug, it is recommended to use a piece of Polycarbonate tube (for example, left over from building a blades with a tube bought at TCSS).
However, if you don't have access to a 7/8 polycarbonate tube (or don't have the required tools), you can buy this tube part in order to build the 7/8" Turbine Blade Plug (part 1/3), This tube is 1.5" long.
Here is a build log: http://goth-customsabers.ftl-network.com/log/turbine-blade-plugs/
The White S&F Plastic won't render the effect as nice as originaly intended tho. You can choose to print in transparent plastic, unfortunately this material is quite expensive (hense better to use a PolyC tube leftover).